"Jezston" wrote in message
...

Good point - the PST was probably originally created back when I was
using Office 2000.

Then an oversized PST is the likely problem. See this:
http://www.slipstick.com/problems/repair2gbpst.asp

When you say 'in use' do you mean when Outlook is running? Or just
generally? Hope it's not the latter!

The former.
--
Brian Tillman [MVP-Outlook]