Qt creator configuration files and debug

Hi to all,
I accidentally deleted the configuration files of qt creator in my home (after a linux reinstallation). Now, every time I try to do a debug by qt creator I obtain:
[QUOTE]This does not seem to be a "Debug" build.
Setting breakpoints by file name and line number may fail.[/QUOTE]
Actually I'm not sure that the problem is in the configuration files (because I don't know if before the reinstalation the debugger worked) but how can I repair it?
Obviously I choose debug version of the project and the problem happen with all qt version installed (4.7.4 and 4.8.1)
thanks in advance

Hi, I did the debug putting
CONFIG += debug
in the project file.
But I can't understand why, also if I choose debug mode, without CONFIG += debug, the project is always compiled in release mode. Indeed the compilator command has the flag (without the debug option in the project file) -DQT_NO_DEBUG
What's wrong? Why QtCreator always compile in release mode?