Using Qt Creator 3.3.0 I get the error 'Unable to create a debugger engine of "no engine"', hovering over the kit shows a message 'Not recognised engine <path>\gdb.exe', I've downgraded to 3.2.2 and it works fine without this error.

(On a related note, using both the Qt 5.4.0 offline installer and web installer, I get an error whilst trying to access qmake.exe saying the process is in use - it's not in use, I can rename the file and whatnot, but regardless Qt installer thinks it's in use, unsure if that's related to this issue or not, I clicked ignore after clicking retry a few times did not sort it)