Found the problem...it was not the SBS 2008 that caused it.... It was my notebook clients - all pre-installed HP notebooks.
I usually uninstall a lot of the software that's pre-installed on the pc's - and some of it (I still don't know what) seems to cause the problem. I think it's the HP ProtectTool... When I roll the pc back to a prevoius state - everything is alright again...
So problem (sort of) fixed :)