Currently I’m working on a product that has been around for a long time, and will be for a lot longer. Even thought 64bit has been out for a long time, this application has it roots in 32bit. This is not necessarily a bad thing, as 64bit will not provide any real processing performance enhancements. Prior to Visual Studio 2010, building with AnyCPU platform configuration was straight forward. Now that we support purely 64bit OS on our server side, things because a little more difficult. Long story short, we needed to configure everything to specify x86. In doing so, we continued to get build errors on our TFS team build server. The error “error CS1607: Assembly generation -- Referenced assembly 'mscorlib.dll' targets a different processor” would show up all over the place. After ensuring that all our projects were set to x86 and the Configuration Manager for debug/release specified x86, we eventually found that the build process MSBuild Platform needed to be set to X86.
As an interesting note, in our researching over x86 and x64, we came across this article AnyCPU Exes are usually more trouble than they're worth. If you’ve been adding new projects in Visual Studio 2010, you’ll notice that they all default to x86.