Sorry I don't have an exact answer for you but I do have a couple of suggestions you should try. Firstly which version of Windows 7 are you using, is it the 7000 Build that was released as a public beta or one of the later 'leaked' versions. There have been a number of strange errors reported with the leaked versions and, as with any pirated software, you should be very careful and are advised against using it at all.
Secondly, have you tried creating a new Administrator account to see if that account is plagued by the same problem? It could be that for whatever reason something has become corrupt in relation to your admin account, so creating a new account should be fine. Thirdly, have you recently installed any new applications specifically that interact with Windows Explorer, for example folder synchronisation tools (like Dropbox, Live Mesh, etc)?
If so it's worth trying uninstalling these and seeing if your problem persists. Fourthly, have you recently performed some windows updates, or had problems doing windows update? If so this link might help chris123nt.com/2009/01/18/sqm-client-cau... I hope those suggestions help in someway but if not I'd recommend waiting until the Windows 7 RC is released to the public on May 5th (2009) and then install that :).