Explorer.EXE - Cannot verify digital signature

I've recently ran the upgrade for the Windows 7 RC from vista business. Now all of the sudden I cannot run many of my programs (especially those that need UAC) because Windows cannot verify the digital signature for this file.

(X)
Windows cannot verify the digital signature for this file. A recent hardware or software change might have installed a file that is signed incorrectly or damaged, or that might be malicious software from an unknown source.

[OK]

This happens with Explorer.EXE when I try to right click on Computer->Manage. It happens with OptionalFeatures.exe when I try to Enable/Disable Windows features from the Control Panel.

I had the Norton Labs UAC installed on Vista. Perhaps that's the problem? Any help is greatly appreciated!

Well see, therein lies the problem. The uninstaller cannot be verified by windows either. It requires UAC. Under these circumstances I couldn't remove it, even if I wanted to.

I did find a solution though:
Boot into safe mode. For some reason, that makes windows skip verification, which allowed me to uninstall Norton UAC. So now it uses regular UAC.

Thanks for the help!