LEADTOOLS DocumentConverter IIS Exception Der Typeninitialisierer für "" hat eine Ausnahme verursacht. ---> .ModuleLoadException: The C++ module failed to load while attempting to initialize the default appdomain. ---> System.Runtime.Serialization.SerializationException: Die Assembly "System.Diagnostics.DiagnosticSource, Version=4.0.2.1, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51" kann nicht gefunden werden.

After deploying a WebApplication which uses the LeadTools 20 DocumentConverter, the application gave me the following exception trying to load my document from a memory stream:

System.TypeInitializationException: Der Typeninitialisierer für "" hat eine Ausnahme verursacht. ---> .ModuleLoadException: The C++ module failed to load while attempting to initialize the default appdomain.
 ---> System.Runtime.Serialization.SerializationException: Die Assembly "System.Diagnostics.DiagnosticSource, Version=4.0.2.1, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51" kann nicht gefunden werden.
Server stack trace:
   bei System.Runtime.Serialization.Formatters.Binary.BinaryAssemblyInfo.GetAssembly()
   bei System.Runtime.Serialization.Formatters.Binary.ObjectReader.GetType(BinaryAssemblyInfo assemblyInfo, String name)
   bei System.Runtime.Serialization.Formatters.Binary.ObjectMap..ctor(String objectName, String[] memberNames, BinaryTypeEnum[] binaryTypeEnumA, Object[] typeInformationA, Int32[] memberAssemIds, ObjectReader objectReader, Int32 objectId, BinaryAssemblyInfo assemblyInfo, SizedArray assemIdToAssemblyTable)
   bei System.Runtime.Serialization.Formatters.Binary.__BinaryParser.ReadObjectWithMapTyped(BinaryObjectWithMapTyped record)
   bei System.Runtime.Serialization.Formatters.Binary.__BinaryParser.Run()
   bei System.Runtime.Serialization.Formatters.Binary.ObjectReader.Deserialize(HeaderHandler handler, __BinaryParser serParser, Boolean fCheck, Boolean isCrossAppDomain, IMethodCallMessage methodCallMessage)
   bei System.Runtime.Serialization.Formatters.Binary.BinaryFormatter.Deserialize(Stream serializationStream, HeaderHandler handler, Boolean fCheck, Boolean isCrossAppDomain, IMethodCallMessage methodCallMessage)
   bei System.Runtime.Remoting.Channels.CrossAppDomainSerializer.DeserializeObject(MemoryStream stm)
   bei System.Runtime.Remoting.Messaging.SmuggledMethodCallMessage.FixupForNewAppDomain()
   bei System.Runtime.Remoting.Channels.CrossAppDomainSink.DoDispatch(Byte[] reqStmBuff, SmuggledMethodCallMessage smuggledMcm, SmuggledMethodReturnMessage& smuggledMrm)
   bei System.Runtime.Remoting.Channels.CrossAppDomainSink.DoTransitionDispatchCallback(Object[] args)
Exception rethrown at [0]:
   bei System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg)
   bei System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type)
   bei System.AppDomain.get_Id()
   bei .DoCallBackInDefaultDomain(IntPtr function, Void* cookie)
   bei .LanguageSupport.InitializeDefaultAppDomain(LanguageSupport* )
   bei .LanguageSupport._Initialize(LanguageSupport* )
   bei .LanguageSupport.Initialize(LanguageSupport* )
   --- Ende der internen Ausnahmestapelüberwachung ---
   bei .ThrowModuleLoadException(String errorMessage, Exception innerException)
   bei .LanguageSupport.Initialize(LanguageSupport* )
   bei .cctor()
   --- Ende der internen Ausnahmestapelüberwachung ---
   bei Leadtools.Document.DocumentFactory.ILcmYy3nX(LoadDocumentData  , Exception  )
   bei Leadtools.Document.DocumentFactory.q3UxSnGHl(Uri  , String  , Stream  , LoadDocumentOptions  , Boolean  )
   bei Leadtools.Document.DocumentFactory.LoadFromStream(Stream stream, LoadDocumentOptions options)

How-i-fixed-it:

I fixed it by adding the System.Diagnostics.DiagnosticSource.dll to the GAC, using an admin command prompt 

**********************************************************************
** Visual Studio 2017 Developer Command Prompt v15.9.3
** Copyright (c) 2017 Microsoft Corporation
**********************************************************************

\bin>gacutil -i System.Diagnostics.DiagnosticSource.dll
Microsoft (R) .NET Global Assembly Cache Utility.  Version 4.0.30319.0
Copyright (c) Microsoft Corporation. Alle Rechte vorbehalten.
Die Assembly wurde dem Cache erfolgreich hinzugefügt.
\DocumentConverter\DocumentConverter\bin>iisreset

I also found how to install an assembly to GAC:
https://stackoverflow.com/questions/9726035/where-can-i-find-gacutil

SQLCLR error: Assembly in host store has a different signature than assembly in GAC. (Exception from HRESULT: 0x80131050)

I was referencing the "System.Drawing" DLL (Version 2.0.0.0) in my SQLCLR Assembly Project.
It was running fine for ages on the Server until i deployed a new version of my Assembly to it today:
Error message when you execute a CLR routine or use an assembly in SQL Server: "Assembly in host store has a different signature than assembly in GAC. (Exception from HRESULT: 0x80131050)"

How-i-fixed-it:
I was able to fix my problem by executing this T-SQL command on my database:

Alter Assembly [System.Drawing]
From 'C:\Windows\Microsoft.NET\Framework\v2.0.50727\System.Drawing.dll'

The issue is also discussed here:
http://social.technet.microsoft.com/Forums/sqlserver/en-US/17df0715-7608-480d-8ad6-78dcf6c9d43a/different-version-in-gac-and-SQL

Link to Microsoft Knowledge Base Article:
http://support.microsoft.com/kb/949080