Hi,
We are using .Net 4 and VS 2010.
As you say, it must have been the x86 target setting that caused the problem (I hope so).
This said, I still cannot open the xlsx from a unit test project - the security error is coming up each time whatever the project settings. I switched to a Windows app for the tests. That is fine for me.
If you google the VerificationException you will find similar problems mostly related to unit test environments. I am wondering if you would see the error when debugging a unit tests.
I will test on another PC and post results tomorrow.
Thanks,
Stephan