This computer for several years has only used Outlook Express as mail handler.
Today (happened before), following Microsoft updates:
On opening OE I got following message:

"OE is not currently your default mail client. Would you like to make it your default mail client?
(tick) Always perform this check when starting Outlook Express"

In the past I have ticked this and opted for OE. This time I opted and didn't tick.
(Note: I opened "Set Program Access and Defaults". This was set at Custom. Among other things I changed the mail client from "Use my current email program" to "Outlook Express". The change was accepted OK and change activity was shown on screen, but when I opened "Set Program Access and Defaults" again it had reverted back to "Use my current email program. Seems strange that it doesn't accept OE. Perhaps this is because I have set as "Custom")

1 Message folder reverted to C:\Docs & Settings\Admin\............................\Micros oft\Outlook Express. In addition today's Inbox filled with new message. My OE doesn't download on opening so even that was ignored.
2 Address Book also changed to MS default.
3 Regedit won't run (to change Address Book back). Nor will Command.
Although I have fixed the Message folder, I have not yet fixed the Address Book because of the Regedit problem.
The change to defaults of the Message Folder and Address Book has happened following the last 3 MS updates, although this is the first time Regedit (and others) refused to run.
There have not been any changes to this computer for some time apart from MS Updates.
Help please