I had the same error and found that the class I was referencing was not the problem, but it had a static variable of another type declared that required another assembly to load. That assembly was built for a target platform of x86 (see Properties-->Build tab) however the main project was compiled for Any CPU. I rebuilt the older assembly for Any CPU... problem solved.
Here are some helpful steps for finding the root cause of this problem...
Click Debug--> Exceptions and check ON all the Thrown checkboxes. This will cause the debugger to stop on all first chance exceptions and will help you find the error under the Type Initializer error that you're seeing. If it is related to another assembly, as mine was, you can use Microsoft's Assembly Binding Log Viewer tool
to help determine the problem.