Can they be opened if they are saved to disk first? I am asking just to help
diagnose the problem. If it cannot be opened after it is saved to disk, can
the same file be opened by other accounts?

Yes, currently and former saved web pages (i.e. on desktop, as *.mht) can
be opened.

*.mhtml and *.eml files from this user account can be opened from other
accounts.


Even a new empty file (empty.txt.mhtml) causes this error at the
problematical user account.
(empty.txt.html (without "m") works like expected.)

:-(


By the way: If I try to open empty.txt.mhtml IE tries for a bunch of
seconds. After a while apparently unsuccessfull the messige "The page cannot
be displayed" appears.

If I rename the mshtml.dll temporarily, of course the file doesn't appear,
but immediatly (no hourglass, no timout period).


So it have to be somthing with the handover to the mhtml handler, I suppose.

Perhaps Security settings? (But IE is reset to defaults completely in this
user account.)