TPL DataFlow error

Hi
I've tried to mock some objects from TPL DataFlow library (can found http://www.microsoft.com/downloads/en/details.aspx?FamilyID=0c52d6cd-2104-4983-9932-930b0225e46e)
and get "System.Security.VerificationException: Operation could destabilize the runtime."
for example - this line
var mocked = isolate.Fake.Instance<ActionBlock<int>>();
or - var mocked = Isolate.Fake.Instance<BufferBlock<int>>();
and so on.
Any ideas?
Thanks
Adiel