Problems archiving sent items

[Seamus]

My autoarchive had been working fine for a number of
months but recently, when the archive is finished,
Outlook throws the following error:

"Error while archiving folder 'Sent Items' in
store 'Personal Folders'"

All other folders archive correctly.

I'm using Outlook 2000 in Internet mail only mode on
Windows 2000. My Sent Items folder contains about 12000
items, my archive.pst is about 400MB and I have about 1GB
free on my HDD.

Any help greatly appreciated

Thanks in advance

Seamus