SGEN: An attempt was made to load an assembly with an incorrect format

I have a project that can build fine on my local machine, however, when I get TFS to build it, I receive the following error -

SGEN: An attempt was made to load an assembly with an incorrect format:

After reading through many other posts here on this topic, most people just say I need to change the build type to either x86 or Any CPU, rather than x64, but after trying countless combinations, this was not the solution. My program is also a windows service, so setting the App Pool to allow 32 bit applications (as suggested by others) is also not the solution.

I encountered this same issue today. A project would not build on my PC but built fine on other PC's

I eventually fixed it by doing the following:

Right-clicked the project with the error, went into Properties

Selected the Build tab and went to the last option which is "Generate serialization assembly" I set this to Off and the project now builds fine.

My problem was finally solved by this page - http://aplocher.wordpress.com/2012/10/12/sgen-an-attempt-was-made-to-load-an-assembly-with-an-incorrect-format-tfs-2010/

Just in case that page ever disappears in the future, here are the steps involved -

1. In Team Explorer, right click on your Build Definition and choose Open Process File Location
2. Double click on the XAML file that is selected
3. In the designer, select the container called Sequence (this is the top-level container that goes around everything else).
4. In the Arguments list (typically at the bottom), change MSBuildPlatform from Microsoft.TeamFoundation.Build.Workflow.Activities.ToolPlatform.Auto to Microsoft.TeamFoundation.Build.Workflow.Activities.ToolPlatform.X86.
5. Save and close the file.
6. Check the file back in to TFS and try your build again.

The problem disappears after installing the latest Windows SDK which includes the 64Bit version of sgen.exe:

http://msdn.microsoft.com/en-us/windows/desktop/bg162891.aspx

Sometimes (if that one does not help) the older version helps:

http://msdn.microsoft.com/en-us/windows/desktop/hh852363.aspx

For some reason the 64bit version of sgen is not included in the Microsoft Build Tools

I found this issue relevant: https://github.com/dotnet/sdk/issues/1630

While waiting for this to be fixed in a future version, I was able to solve the problem by adding two targets to the csproj file, as suggested by https://github.com/joperezr:

<Target Name="RemoveDesignTimeFacadesBeforeSGen" BeforeTargets="GenerateSerializationAssemblies">
    <ItemGroup>
    <ReferencePath Remove="@(_DesignTimeFacadeAssemblies_Names->'%(OriginalIdentity)')" />
    </ItemGroup>
    <Message Importance="normal" Text="Removing DesignTimeFacades from ReferencePath before running SGen." />
</Target>

<Target Name="ReAddDesignTimeFacadesBeforeSGen" AfterTargets="GenerateSerializationAssemblies">
    <ItemGroup>
    <ReferencePath Include="@(_DesignTimeFacadeAssemblies_Names->'%(OriginalIdentity)')" />
    </ItemGroup>
    <Message Importance="normal" Text="Adding back DesignTimeFacades from ReferencePath now that SGen has run." />
</Target>