Can't open message history

I can't determine when the problem first occurred -whether at the
upgrade from Messenger to 'Live Messenger' or when IE7 was installaed,
BUT . . . .

- I can no longer see my 'full' history in Messenger, though the last
exchange always appears - when I click 'view entire history' I
eventually get a message to the effect that the file is not currently
available and a suggestion to 'try again later'.
- I cannot open the xml history file by clicking on it under Windows
Explorer either.

I CAN import the file into Excel, using the default style ***.
Everything is there.

I HAVE reinstalled Internet Explorer 7 with no change
I have NOT tried to reinstall MSN messenger, since the file itself
doesn't open under IE or under Messenger it didn't seem to be a
reasonable step..

I have tried reregistering the xml dll using the "regsvr32 msxml3.dll"
command.

Any suggestions?

.