CLR Profiling API and "unhandled exception in unknown module"

Hi!
I'm trying to use the CLR Profiling API on a WPF process and something strange happens.
When I run the WPF process in a normal way it runs fine.

But when I run it with the evnironment variables of my profiling DLL, I get the following exception:

An unhandled exception of type 'System.IO.FileLoadException' occurred in Unknown Module.
Additional information: Hash validation failed for file or assembly 'PresentationFramework, Version=4.0.0.0

(I managed to find it after attaching to the WPF process with a debugger)

When I try profile a winforms application it doesn't happen.

Why is it happening and how can I fix it?

thanks :)