Using CRM 4.0 assemblies on a CRM 2011 Server

CRM 2011 Server includes a publisher policy that causes any assembly built against the CRM 4 sdk assemblies to load the CRM 5 sdk assemblies instead. There are certain circumstances where this can cause errors loading the assembly; see the end of this post for possible error messages.

One workaround is to not run the application on a Crm 2011 Server, but there is an alternative, which is to explictly tell your application not to use this publisher policy file. This is done through adding the following to the app.config file:

<runtime>
<assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
<dependentAssembly>
<assemblyIdentity name="Microsoft.Crm.Sdk" publicKeyToken="31bf3856ad364e35" culture="neutral" />
<publisherPolicy apply="no" />
</dependentAssembly>
</assemblyBinding>
</runtime>

This raises one more issue: in some circumstances your assembly may not be the main .exe, but a .dll loaded by another process, in which case you'll have to modify/create the .config file for that .exe. This is done by creating a file named .exe.config in the same directory as the .exe (here's an example). I have a nagging concern that I may have to do this with SSIS packages that use a custom component that use the SDK assemblies, which could get interesting, as different executables are used for in design, debug and runtime. If I do have this issue with SSIS, then I'll post a more detailed workaround (if I find it).

My hope is that this is a temporary problem that will be fixed, as the readme in the 5.0.1 version of the SDK refers to an 'incorrect Publisher Policy'. This readme also gives an explanation of this issue

One possible error
System.IO.FileLoadException: Could not load file or assembly 'Microsoft.Crm.Sdk, Version=5.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
File name: 'Microsoft.Crm.Sdk, Version=5.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' ---> System.IO.FileLoadException: Could not load file or assembly 'Microsoft.Crm.Sdk, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
File name: 'Microsoft.Crm.Sdk, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'

Another possible error
System.IO.FileNotFoundException: Could not load file or assembly 'Microsoft.Crm.Sdk, Version=5.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.
System.IO.FileNotFoundException: Could not load file or assembly 'Microsoft.Crm.Sdk, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.