SBS 2008 queries WSUS for missing updates on the network. If you install WSUS 3 SP2 and your WSUS database has never been purged, the daily SBS reporting may stop working.
The fix? Open up the WSUS console, go to Options and run the Server Cleanup Wizard. However, on the first time, don’t run the wizard with all the options checked. You’ll find it it won’t finish. Run each option independently. The first option, Unused updates and update revisions, will take a long, long time. So be patient. Do it on a weekend.
Once the WSUS cleanup is done, reporting should be back to normal.