c# - InvalidCastException for two Objects of the same type

Question

I have this weird problem that I cannot handle myself. A class in the model of my mvp-project designed as singleton causes an InvalidCastException.

The source of error is found in this code line where the deserialised object is assigned to the instance variable of the class: engineObject = (ENGINE)xSerializer.Deserialize(str);. It occurs whenever I try to add one of my UserControls to a Form or to a different UC. All of my UCs have a special presenter that accesses the above mentioned instance variable of the singleton class.

This is what I get when trying to add a UC somewhere:

'System.TypeInitializationException: The type initializer for 'MVP.Model.EngineData' threw an exception. ----> 

System.InvalidCastException: [A]Engine cannot be cast to [B]Engine. Type A originates from 'MVP.Model, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' in the context 'LoadNeither' 
   at location '[...]AppDataRoamingMicrosoftVisualStudio9.0ProjectAssembliesuankw1hh01MVP.Model.dll'. 
Type B originates from 'MVP.Model, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' in the context 'LoadNeither' 
   at location '[...]AppDataRoamingMicrosoftVisualStudio9.0ProjectAssembliesu_hge2de01MVP.Model.dll'
...

So I somehow have two assemblies and they are not accessed from my project folder, but from a VS temp folder? I googled a lot and only found this: IronPython Exception: [A]Person cannot be cast to [B]Person. There is a solution offered, but it concerns IronPhyton and I don't know where to use it within my project.

Answer 1

Types are per-assembly; if you have "the same" assembly loaded twice, then types in each "copy" of the assembly are not considered to be the same type.

These issues normally crop up when the two assemblies are in the Load and LoadFrom contexts. See

Difference between LoadFile and LoadFrom with .NET Assemblies?

and the link to suzcook's blog for details on that issue.

Also, consider using the fusion log viewer to help diagnose the problem.

http://msdn.microsoft.com/en-us/library/e74a18c4%28VS.71%29.aspx