I'm pretty sure it's related to one of the values in the registry that got changed by a recent Windows update since it screwed up some of my other shell extensions and context menu handlers too. I really don't know which ones specifically but I have a couple of registry fixes for some other software with the same problem and they both refer to this:
http://groups.google.com/group/micro...a2c760b7ade4e0
btw, on my machine, it was MS update KB908531 with the verclsid.exe update that changed the "approved, blocked, and cached" keys under "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Shell Extensions"