Mail security for Exchange 6.5 - High CPU usage

[APM 2]

I upgraded from mail security 4.5 to 6.5 recently.  Since then I've noticed the server is thrashing the CPU in the first part of each morning; services.exe and ekrn.exe taking 100 percent between them.  At some point it does settle down for the day but while the CPU usage is so high the Outlook clients are predictably slow to retrieve messages.

Its a single core Windows and Exchange server 2003 box (yes, I know).

Any ideas?

[APM 2]

This appears to have been caused by the default scheduled task which triggers a file system scan after signature updates.  Disabling this task has so far solved the issue.

[APM 2]

Update; the behaviour has returned so is not resolved.

Any suggestions are welcome!