Regularly, when I click a "mailto:..."-link on some webpage I get the
error message
"Could not perform this operation because the default mail client is not
properly installed".

Needless to say, that "Microsoft Outlook" is of course selected under
Tools = Internet Options = Programs = E-mail.

Puzzled I investigated further and found that in Explorer under Tools =
Folder Options... = File Types the entry for "(None] URL:MailTo
Protocol" contains the value
"C:\PROGRA~1\MICROS~2\Office10\OUTLOOK.EXE" -c IPM.Note /m "%1" (i.e. in
8.3 notation).

If I change this entry to use long filenames, i.e.:
"C:\Program Files\Microsoft Office\Office10\Outlook.exe" -c IPMNote /m
"%1"

and then click on such a MailTo-URL then things work as expected, i.e.
Outlook starts up and opens a new email with the recipient already
entered.

But after the next reboot that darn value is back to
"C:\PROGRA~1\MICROS~2\Office10\OUTLOOK.EXE" -c IPMNote /m "%1"

again and and things don't work any more.

So:
1.) Who/what is changing this value back???
2.) why does the short (8.3) form of the path not work here?

Any ideas or hints anybody?

Michael