At the office I’m using Windows Vista 64 bit, we had a lot of bad surprises when it came to combine 32 bit DLLs from Oracle client with 64 bit DLLs of the projects. The most common exception in which we bumped was “Invalid image format”. We were using Oracle which is a 32 bit client. To solve the issue we had to migrate to Oracle client which has support for 64 bit applications. Once we did this we have discovered other inconvenient, PL/SQL didn't worked at all, the reason…it required a 32 bit Oracle client to be installed on the machine. The only solution found by one of my colleagues is that beside Oracle client we should install also Until now everything works just fine. By the way, same thing applies also to TOAD.