Outlook Express not saving news messages

After reformatting and updating etc a month or so ago, I came to setup
OE for newsreading just the other day. Account setup fine (as I've
always done it), and subscribed to the groups I wanted to. I
downloaded a 100 or so headers for each of the 4 groups I wanted.
Looked at a few, then came up with an error in the Preview pane
"Message could not be displayed
Outlook Express encountered an unexpected problem while displaying
this message. Check your computer for low memory or low disk space and
try again."
Click on another newsgroup didnt change the whole window display.
Clicking on Inbox, Sent item and all the other folders made no
difference either. Neither could I get a right-click menu up. Clickin
on the Creat Mail button produced an error: "There was an error
opening this message. An error has occurred" As such I was forced to
close and reopen OE. On doing so, all those headers I'd downloaded had
disappeared, so I grabbed them again. Once more, for no reason, I got
the same error in the Preview pane.
I have 12GB of free HDD space, with 1GB of memory.
This has never happened before. Does anyone have any ideas why this
might be happening? I'm uptodate with all security patches, etc

Thanks
GF