Check your system for Security Patch #821557, while we've only seen this
issue on SP1 systems, it's possible it might also happen on system not
upgraded. There is a problem with that patch that causes the symptoms you
describe. Go to Add/Remove Programs in Control Panel, scroll your list for
"hotfixes" and see if such a number is referenced there.
If you don't see it, go to Windows update, let it scan your system, when
finished, look for update history in the left pane and look for that
security patch as it should tell you the reference number in Add/Remove.
When you find it, use Add/Remove to remove it or use System Restore to take
you back to a time prior to when that patch was installed. Start\All
Programs\Accessories\System Tools\System Restore.
