My service is packed, I'm ready to go
...installing here, upgrade once more
(Adapted from "Leaving on a Jet Plane")
A post on the Visual Studio Team System forums reminded me of one very important tidbit of Visual Studio patching. The integration of Team Foundation Server with Visual Studio enables all sorts of marvelous functionality and is great for development, but does place some restrictions on what patching scenarios are supported.
In particular, all Visual Studio derived products on the same machine must have the same service pack level. This includes Visual Studio Express SKUs, Visual Studio Standard, Professional, Team System (and the individual role SKUs), Team Foundation Server's Application Tier, Data Tier (only exists in TFS 2005), Team Build, Proxy, and Team Explorer. Since these components share common assemblies, if one tool has been upgraded to SP1 while another is still at RTM the functionality is undefined and unsupported.
The easiest way to check your SP level is look in the control panel Add/Remove Programs (on XP/Server 2003) or Programs and Features (on Vista/Sever 2008). For the former, check the "Show updates" button. On the latter, click the "View installed updates" link. There, you should be able to see which components have been updated and which haven't. If there's a mismatch, my recommendation is to reapply the Visual Studio and TFS service packs to bring everything back up to the latest SP. Of course, you can also uninstall the SP from everywhere that it's installed, but I would hope you'd want to get the latest and greatest functionality!
Best of luck, folks, and feel free to shoot along questions and comments if there's any other topics you want to see me address.