If you get an error like this:
The system cannot find the path specified.
or like this:
error MSB6006: "cmd.exe" exited with code 3.
Then you may need to just change your Qt Version under Qt Project Settings. The trick is that you must change from one valid Qt Version to another valid Qt Version. For example, if your current version is set to $(DefaultQtVersion) then you should change it to the explicit version entry. Make sure you actually apply the changed setting because otherwise nothing will happen. Once you have changed and applied the new setting, you can change it back and it may fix the problem.