It happened because I was trying to eliminate another C++ module after porting it to C#, but a 32-bit build of the module was still lying around after I deleted its C++ project, and it ended up getting copied to the 64-bit server, which wasn't happy about that at all.
Although I've now taken preventative measures so it won't happen again, there are basically no C++ modules left now, so it's kind of moot.
