I got an error about the cab PCW_CAB_VS_10260 being corrupt while adding a feature to my Visual Studio 2005 installation. The installation had been updated to SP1, so my guess was that this was somehow due to me trying add a feature to my SP1 updated VS 2005 installation while using the original VS 2005 installation discs.

My solution: Uninstall VS 2005. Reinstall it with all the features I needed. Install SP1.

Yes, it sucks. But it worked.

And one last thing, an alternative solution that may work but that I didn’t try would be to add features using a VS 2005 disc or installation that has SP1 slipstreamed. It’s worth a try.