problems upgrading Qt from 2.4.1 to 2.5.0

hi
I had this on line application divided into 2 parts, client and server. The program worked fine until I decide to upgrade Qt from version 2.4.1 to 2.5.0, I tried using the updater but it told me that it didn't find any update so I decided to uninstall Qt (always with the maintance tool) and then reinstall the new version. after doing this, I tried launching my application again. The program compiled with out problems but when I tried sending an expression ( my application design's a graphic from an expression) from the client to the server a message box popped up telling me debug assertion failed. Expression:string substring out of range press retry to debug the application. If I press retry the program just crashes but If i press ignore a couple of times then the program sometimes will work and other's won't. If I try debugging the following message comes up

The debugger engine 'Cdb engine' required for debugging binaries of the type 'x86-windows-msvc2010-pe-32bit' is not configured correctly.

can somebody give a hint because it's very annoing!
I tried uninstalling and reintalling the SDK but nothing changed!
thank's

Please do not confuse "Qt" with "Qt Creator". If you upgrade Qt Creator, it has no influence on your application. Please check which version of "Qt" you had before (e.g. 4.7.4) and which you have now (e.g. 4.8.0).

I had 4.7.4 and now I have 4.8.1

Rebuild and run the application from the command line, see if the wrong behaviour persists. If so, debug from within the commandline or a graphical frontend to your debugger.