I found that Qt Creator 2.6.0 doesn't run qmake for the windows installation. If you do this at the command-line and build from Qt Creator with the resulting Makefile you can then load the .exe file target when Qt Creator tries to run .exe.
Once you have done this once, ie. the Makefile exists and .exe file setup in Qt Creator it works fine.
I set the Windows user Environment variable $PATH to include C:\Qt\4.8.3\bin but not sure if that was necessary. The windows installation of Qt shouldn't have these problems.