I have this same problem..and the above response wasn't as helpful as I'd hoped (but thanks!)
When I run Ccleaner, i get a notifcation that there is a corrupted file in the temporary internet files\IE5 folder\L0N56724 (or something close to that)
The folder cannot be deleted (even using Unlocker). I've set Ccleaner to run on startup too, hoping this would catch the problem, but it does not.
Has anyone found a fix to this problem?