Have you updated to After Effects CS4 (9.0.2)? That update fixes a lot of problems.
Has this problem always occurred, or did it start recently? If it only started recently, what changed in your computer system immediately before this started happening?
> i read somewhere that i need to disable the openGL but i cant because i need it
Why do you think that you need it? OpenGL rendering is only useful for preview renders, and it often causes a lot of problems. If you're having problems, disabling OpenGL rendering is one of the first things to try. See "Troubleshoot OpenGL problems".
Keylight is a memory hungry monster, so it is quite possible it is simply running out of memory on your system. These crashes have been quite frequent in the past... Of course run any updates, but that may not at al lresolve the issue, so using anotehr keyer like Primatte might be necessary...
i have this problem for about 2 month now but lately the After crashes more often.
well i will try to disable openGL, thanks.