Hello Tim,
You need to make sure that all assemblies have the same version. You can check this in Visual Studio (see attached image). Please note that the version that ends with 20 should be used when you target framework is .Net 2.0 to 3.5. The version that ends with 40 should be used for .Net 4.0 or newer.
I hope this will be useful. Let me know if you have additional questions.
Regards,
Dimitar
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