diff --git a/Creator/ApplicationArguments.cs b/Creator/ApplicationArguments.cs
index 9887437..de8e933 100644
--- a/Creator/ApplicationArguments.cs
+++ b/Creator/ApplicationArguments.cs
@@ -1,4 +1,3 @@
-using System.Collections.Generic;
 using System.ComponentModel;
 using System.IO;
 
diff --git a/Katteker.Test/testdata/squirrelHelperInfo.json b/Katteker.Test/testdata/squirrelHelperInfo.json
index d1428ad..9e26dfe 100644
--- a/Katteker.Test/testdata/squirrelHelperInfo.json
+++ b/Katteker.Test/testdata/squirrelHelperInfo.json
@@ -1,6 +1 @@
-<?xml version="1.0" encoding="utf-8"?>
-<configuration>
-    <startup> 
-        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5"/>
-    </startup>
-</configuration>
+{}
\ No newline at end of file
diff --git a/Katteker/Katteker.csproj b/Katteker/Katteker.csproj
index 6666e5f..4aa8f77 100644
--- a/Katteker/Katteker.csproj
+++ b/Katteker/Katteker.csproj
@@ -43,6 +43,7 @@
     <Compile Include="Constants.cs" />
     <Compile Include="KattekerConfig.cs" />
     <Compile Include="Common\MarkdownSharp.cs" />
+    <Compile Include="KattekerUpdateException.cs" />
     <Compile Include="UpdateInfo.cs" />
     <Compile Include="UpdateManager.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
diff --git a/Katteker/KattekerUpdateException.cs b/Katteker/KattekerUpdateException.cs
new file mode 100644
index 0000000..5e383fb
--- /dev/null
+++ b/Katteker/KattekerUpdateException.cs
@@ -0,0 +1,24 @@
+using System;
+
+namespace Katteker
+{
+    /// <summary>
+    /// Represent an error message in the Katteker update process.
+    /// </summary>
+    public class KattekerUpdateException : Exception
+    {
+        /// <summary>
+        /// Creates a new instance of the <see cref="KattekerUpdateException"/> class with the error message.
+        /// </summary>
+        public KattekerUpdateException(string message) : base(message)
+        {
+        }
+
+        /// <summary>
+        /// Creates a new instance of the <see cref="KattekerUpdateException"/> with the error message and inner exception.
+        /// </summary>
+        public KattekerUpdateException(string message, Exception innerException) : base(message, innerException)
+        {
+        }
+    }
+}
\ No newline at end of file
diff --git a/Katteker/ReleaseEntry.cs b/Katteker/ReleaseEntry.cs
index 1797cae..4c9e687 100644
--- a/Katteker/ReleaseEntry.cs
+++ b/Katteker/ReleaseEntry.cs
@@ -6,6 +6,7 @@ using System.Text.RegularExpressions;
 
 namespace Katteker
 {
+    /// <inheritdoc cref="IComparable" />
     /// <summary>
     /// Entry of a Release.
     /// </summary>
@@ -16,7 +17,7 @@ namespace Katteker
         private const char Seperator = '|';
 
         /// <summary>
-        /// Construct a new release entry.
+        /// Creat an instance of <see cref="ReleaseEntry"/>.
         /// </summary>
         public ReleaseEntry(string filename, SemVersion version, long fileSize, bool isDelta, string sha1)
         {
@@ -28,18 +29,25 @@ namespace Katteker
         }
 
         /// <summary>
-        /// Construct release entry from string.
+        /// Create an instance of <see cref="ReleaseEntry"/> from string.
         /// </summary>
-        /// <exception cref="FileLoadException"></exception>
+        /// <exception cref="ArgumentOutOfRangeException">Argument 'line' has not the right format.</exception>
+        /// <exception cref="ArgumentNullException">Argument 'line' is null.</exception>
+        /// <exception cref="FileLoadException">Filename is not compliant.</exception>
         public ReleaseEntry(string line)
         {
-            var elements = line?.Split(Seperator);
-            if (elements?.Length != 3) return;
+            if (line == null) throw new ArgumentNullException(nameof(line));
+            var elements = line.Split(Seperator);
+            if (elements.Length != 3)
+            {
+                throw new ArgumentOutOfRangeException(nameof(line), elements.Length, "The release entry has not the right format.");
+            }
+
             SHA1 = elements[0];
             Filename = elements[1];
             Filesize = long.Parse(elements[2]);
             var fileSegments = Regex.Match(Filename, FilenameRegex);
-            if (fileSegments.Groups.Count < 3) throw new FileLoadException("Filename not compilant.");
+            if (fileSegments.Groups.Count < 3) throw new FileLoadException("Filename is not compilant.");
             ApplicationName = fileSegments.Groups[1].Value;
             Version = SemVersion.Parse(fileSegments.Groups[2].Value);
             IsDelta = fileSegments.Groups[3].Value != "full";
diff --git a/Katteker/Releases.cs b/Katteker/Releases.cs
index 668274b..3019011 100644
--- a/Katteker/Releases.cs
+++ b/Katteker/Releases.cs
@@ -13,11 +13,11 @@ namespace Katteker
     {
         private readonly string _filePath;
 
-        private SortedList<SemVersion, ReleaseEntry> ReleaseEntries { get; }
+        private SortedDictionary<SemVersion, ReleaseEntry> ReleaseEntries { get; }
 
         private Releases()
         {
-            ReleaseEntries = new SortedList<SemVersion, ReleaseEntry>();
+            ReleaseEntries = new SortedDictionary<SemVersion, ReleaseEntry>();
         }
 
         /// <summary>
@@ -52,7 +52,7 @@ namespace Katteker
         /// </summary>
         public void WriteReleaseFile()
         {
-            File.WriteAllLines(_filePath, ReleaseEntries.Select(x => x.Value.EntryAsString));
+            File.WriteAllLines(_filePath, ReleaseEntries.Values.Select(x => x.EntryAsString));
         }
 
         /// <summary>
@@ -67,16 +67,8 @@ namespace Katteker
             var setupFile = new FileInfo(setupFilePath);
             var entry = new ReleaseEntry(setupFile.Name, version, setupFile.Length, false, sha1);
 
-            if (!ReleaseEntries.ContainsValue(entry))
-            {
-                if (ReleaseEntries.ContainsKey(version))
-                {
-                    ReleaseEntries.Remove(version);
-                }
-
-                ReleaseEntries.Add(version, entry);
-            }
-
+            if (ReleaseEntries.ContainsValue(entry)) return entry;
+            ReleaseEntries[version] = entry;
             return entry;
         }
 
diff --git a/Katteker/UpdateManager.cs b/Katteker/UpdateManager.cs
index 43795e6..d0cf4a9 100644
--- a/Katteker/UpdateManager.cs
+++ b/Katteker/UpdateManager.cs
@@ -20,12 +20,11 @@ namespace Katteker
         private readonly string _applicationName;
         private readonly string _packageDir;
         private readonly string _rootAppDirectory;
-        private readonly string _urlOrPath;
         private Releases _releases;
 
         private UpdateManager(string urlOrPath, string applicationName, string rootDirectory)
         {
-            _urlOrPath = urlOrPath;
+            UrlOrPath = urlOrPath;
             _applicationName = applicationName;
             _rootAppDirectory = rootDirectory;
             var packageDir = Path.Combine(rootDirectory, Constants.PackageFolder);
@@ -41,7 +40,7 @@ namespace Katteker
         /// <summary>
         /// Url or path where the update files are located.
         /// </summary>
-        public string UrlOrPath => _urlOrPath;
+        public string UrlOrPath { get; }
 
         /// <summary>
         /// Create the update manager.
@@ -50,7 +49,8 @@ namespace Katteker
         /// <param name="applicationName">name of the application to update.</param>
         /// <param name="rootDirectory">root directory.</param>
         /// <returns>the update manager.</returns>
-        public static UpdateManager Create(string urlOrPath = null, string applicationName = null, string rootDirectory = null)
+        public static UpdateManager Create(string urlOrPath = null, string applicationName = null,
+            string rootDirectory = null)
         {
             _config = ReadConfigFile();
             urlOrPath = urlOrPath ?? _config.Publish;
@@ -67,7 +67,8 @@ namespace Katteker
         /// <param name="applicationName">name of the application to update.</param>
         /// <param name="rootDirectory">root directory.</param>
         /// <returns>true if the creation success, false otherwise.</returns>
-        public static bool TryCreate(out UpdateManager manager, string urlOrPath = null, string applicationName = null, string rootDirectory = null)
+        public static bool TryCreate(out UpdateManager manager, string urlOrPath = null, string applicationName = null,
+            string rootDirectory = null)
         {
             try
             {
@@ -87,7 +88,21 @@ namespace Katteker
         /// <returns></returns>
         public async Task<IEnumerable<ReleaseEntry>> CheckForUpdateAsync()
         {
-            _releases = Utility.IsWebUrl(_urlOrPath) ? await DownloadIndexAsync(_urlOrPath).ConfigureAwait(false) : GetFromFilesystem(_urlOrPath);
+            try
+            {
+                return await CheckForUpdateImplAsync().ConfigureAwait(false);
+            }
+            catch (Exception e)
+            {
+                throw new KattekerUpdateException("Error at checking for available update.", e);
+            }
+        }
+
+        private async Task<IEnumerable<ReleaseEntry>> CheckForUpdateImplAsync()
+        {
+            _releases = Utility.IsWebUrl(UrlOrPath)
+                ? await DownloadIndexAsync(UrlOrPath).ConfigureAwait(false)
+                : GetFromFilesystem(UrlOrPath);
             var updateInfo = new UpdateInfo(_applicationName, _releases);
             return updateInfo.ReleasesToApply;
         }
@@ -114,12 +129,19 @@ namespace Katteker
         /// <returns></returns>
         public async Task<bool> UpdateAppAsync(IProgress<int> progress = null)
         {
-            progress?.Report(0);
-            var updateEntries = (await CheckForUpdateAsync().ConfigureAwait(false)).ToArray();
-            var update = updateEntries.LastOrDefault();
-            if (update == null) return false;
-            progress?.Report(30);
-            return await UpdateAppImplAsync(update, progress).ConfigureAwait(false);
+            try
+            {
+                progress?.Report(0);
+                var updateEntries = (await CheckForUpdateAsync().ConfigureAwait(false)).ToArray();
+                var update = updateEntries.LastOrDefault();
+                if (update == null) return false;
+                progress?.Report(30);
+                return await UpdateAppImplAsync(update, progress).ConfigureAwait(false);
+            }
+            catch (Exception e)
+            {
+                throw new KattekerUpdateException("Error at updating application.", e);
+            }
         }
 
         private static async Task<Releases> DownloadIndexAsync(string urlOrPath)
@@ -151,11 +173,9 @@ namespace Katteker
             foreach (var process in Process.GetProcessesByName(_applicationName))
             {
                 var path = Path.GetDirectoryName(process.MainModule.FileName);
-                if (_rootAppDirectory.Equals(path))
-                {
-                    process.Kill();
-                    return Task.Delay(500);
-                }
+                if (!_rootAppDirectory.Equals(path)) continue;
+                process.Kill();
+                return Task.Delay(100);
             }
 
             return Task.FromResult(true);
@@ -165,42 +185,39 @@ namespace Katteker
         {
             var targetFile = Path.Combine(_packageDir, filename);
             File.Delete(targetFile);
-            if (Utility.IsWebUrl(_urlOrPath))
+            if (Utility.IsWebUrl(UrlOrPath))
             {
-                var url = _urlOrPath.TrimEnd('/');
+                var url = UrlOrPath.TrimEnd('/');
                 url += "/" + filename;
                 await new WebClient().DownloadFileTaskAsync(new Uri(url), targetFile).ConfigureAwait(false);
             }
             else
             {
-                File.Copy(Path.Combine(_urlOrPath, filename), targetFile);
+                File.Copy(Path.Combine(UrlOrPath, filename), targetFile);
             }
         }
 
         private async Task<bool> UpdateAppImplAsync(ReleaseEntry lastEntry, IProgress<int> progress)
         {
-
+            if (lastEntry == null) throw new ArgumentNullException(nameof(lastEntry));
             var targetFile = Path.Combine(_packageDir, lastEntry.Filename);
             //download file.
             await PutFileInPackageFolderAsync(lastEntry.Filename).ConfigureAwait(false);
             progress?.Report(60);
 
-            if (!VerifyFileChecksum(targetFile, lastEntry.SHA1)) throw new FileLoadException();
+            if (!VerifyFileChecksum(targetFile, lastEntry.SHA1)) throw new FileLoadException("Checksum missmatch.");
             progress?.Report(70);
 
             await KillAppStubAsync().ConfigureAwait(false);
             progress?.Report(80);
 
-            using (var updater = new Process())
+            using (var updater = Process.Start(targetFile, "/S"))
             {
-                updater.StartInfo = new ProcessStartInfo(targetFile, "/S");
-                updater.Start();
-                updater.WaitForExit();
+                updater?.WaitForExit();
             }
 
             progress?.Report(100);
-
             return true;
         }
     }
-}
+}
\ No newline at end of file