WSUS 3.0 WSUSService crash

Hi all,
I am using WSUS3.0 in Windows Server 2003 SP1 running in VMware.
Somehow synchronizing fails for over than a month because WSUSService
crashes.

I can restart WSUSService manually by typing "net start WSUSService" in
command line, but whenever it is synchronizing it fails between 10% and 15%.

However Catalog synchronizes successfully (getting msg 10021).

Syslog has some errors concerning WSUS:
10032 (Server cant download some updates)
364 (... File cert failure ...)
5144 (... SUSDB was cancelled by user or timed out after 1047 ms...)

7034 (Service "Update Service" exited unexpected. This already happened
13Times)

Does anybody have an idea how I can fix this?