Call of Duty 4: Modern Warfare couldn't write a file. ????

I recently re-installed CoD4 and updated to current patch.

Now every time I try to start the game I get the following error msg.

"Call of Duty 4: Modern Warfare couldn't write a file. The hard drive is probably full."

There is 350GB free space on my harddrive.
Running Vista 32 system, 4GB ram, C2D 3.0 Ghz, 8800GTX, 500GB HD.

Any ideas?

Thanks in advance!