I can't reproduce a problem *upgrading* a 32-bit project to a 64-bit project ("Upgrade project to Win64").
Did you use that, or just changed the machine setting in the project settings ("compiler" and "linker" tabs)? This is trickier since the macro "POC_PROJECT_TYPE" may or may not get updated - it must be >=10 for a 64-bit project to work correctly in all cases. I may see a problem here...