My copy of Worms 4 Mayhem stopped working after upgrading my graphic card.

The game stops loading after the movies and the "loading "sentry" page", and gets back to Windows with message "Worms 4 Mayhem encountered an error and has to close".

My graphic card is an ATI Powercolor X1650 Pro, all drivers are up-to-date.
I can run a very recent game PES 2009) thanx to GraphCard update, so i don’t feel like downgrading…

Here are my specs :
AMD Athlon XP 2600+
2,08GHZ 1,50 Go RAM
Windows XP Pro sp2

What i tried already :
-Upgrading Graphic Cards Drivers,( I deleted old ones with Driver Sweeper)
-Installing again motherboard drivers
-Uninstall/reinstall game
-Launching game with every config possible (movies, resolution, etc…)
-Lauching game with and without old SaveGame.xom
- Cleaning up the Starforce protection program and reinstalling it

Thanx in advance for your help