Spring RTS Engine

When i first boot up my pc and play spring i have around 150-250 FPS, but the screen will flicker randomly, and eventually crash giving me a runtime error. When i join another game my FPS has dropped to 25-50.. I don't understand it at all, ive tried all different settigns for spring + the nvidia ctrl panel, all gives same result.

Any help/advice appreciated, thanx

Running -
AMD sempron 3400+
Nvidia Geforce 7600 GS
512 MB ram

Make sure you have the most uptodate drivers and check out this thread. Also don't use dynamic water, use refractive + reflective.