I also had a nasty error that said that it couldn't find the entry point of a throw exception in libstdc++-6.dll in both the QT compilation and the protobuf compilation. I found that I had to delete libstdc++.dll inside of C:\mingw32\lib\gcc\i686-w64-mingw32\4.9.2 because it was trying to link against a different version of std c++ lib which already exists as libstdc++-6.dll inside of C:\mingw32\bin