See:

All e-mail items may be missing when you start Outlook Express 6 Service
Pack 1:
http://support.microsoft.com/Default.aspx?kbid=918069
--
~Robear Dyer (PA Bear)
MS MVP-Windows (IE/OE, Shell/User, Security), Aumha.org VSOP, DTS-L.org


Larry wrote:
I downloaded KB918766 to automate the registry counter reset after manual
compacting. Everything seemed to work fine, except I noticed that during
the compacting a Copying window popped up from time to time. Is that
normal behavior? I had never seen that before I downloaded the Hotfix.
Thanks. Larry