If trying to open a project when MAKEFILE_GENERATOR is set to MSVC:
"Qmake spec sets an invalid MAKEFILE_GENERATOR."
Can be reached by the following steps:
1) Build Qt 4.6.2 from source by MSVC2010 compiler.
2) Run Qt Creator 3.4.1 and change setting for Qt 4.6.2 build above.
3) Open the sample (examples/widgets/analogclock) bundled with Qt 4.6.2.
Can be fixed by having MSVC (in addition to the MSVC.NET) in src/shared/proparser/spec_post.prf