The uninstd.h header is there, I can link to it fine. Like I said, I can compile if I comment out the include statement for QApplication, but then I can't use processEvents, which I need so that the loop is able to send the signal to the calling thread. Without it, the signal UpdateProgress() never gets received. I tried changing the order of the include statements the way totem suggested, and I went from a few compile errors to hundreds. I got multiple definition errors for just about every Qt function on the face of the earth. It's almost like different sections of the code are linking to different versions of Qt, but I only have one on my system, 4.6.3 with Qt Creator 2.0. Thanks for the suggestions. I can post more code or compiler output if that would help.