I have three qt versions

c:\qt\4.5.2 - qt installed by installer
c:\qt\4.5.2-gcc - qt compiled from sources in z:\qt-src using mingw gcc 4.4.0
c:\qt\4.5.2-vc - qt compiled from sources in z:\qt-src using vc++ from vs2008

When I'm setting them in Qt Creator I get the error
"[one of the above three paths] is not a valid Qt directory"

What constitutes valid (from Qt Creator point of view) Qt folder end where can I find documentation on this subject?