Hi!
I have no 64bit machine available, so I can't test this specific problem.
Are you sure that you have set the Platform target to x86 in the Build tab from the Project's settings?
In this blog post it's described in more detail: http://www.hanselman.com/blog/BackToBasics32bitAnd64bitConfusionAroundX86AndX64AndTheNETFrameworkAndCLR.aspx
Best regards,
Alex