Seems like some update that WSUS pulls down automatically has caused an issue with the SBS reporting. We have seen something similar when there have been OEM issues with WSUS. For more information we suggest you take a look at the official SBS Blog posting. which should give you everything you need to know.
The solution appears to be that under WSUS 3.0 you force a resync from the console. since this can't be done with the standard WSUS 2.0 on SBS 2003 R2, the best bet appears to be simply to wait for WSUS to resync with the server. Admittedly, it is a bit of fingers-crossed scenario but for the time being their doesn't appear to be much choice.
In all honesty, can't say that we like or use WSUS that much at all. There are far better solutions from third parties out there. True, you have to pay fro them but when you look at the additional functionality and flexibility it is well worth the investment.
Also reading Susan Bradley's blog, seems that SBS R2 installations are not the only ones experiencing issues. See the following Computerworld article for the impact on enterprise users. And all of this the day before patch Tuesday - Yeah WSUS !!!
The Microsoft WSUS have now posted an official response to the WSUS issue. You can find it here.