Outlook 2007 is Synchronizing Folders

Everytime I download mail, I get an icon that appears in the system
tray. The icon is animated. Mousing over the
icon it says:

"Microsoft Office Outlook is synchronizing folders"

This synchronizing causes the PC to hang until it completes. What is it synchronizing?

Please can you tell me how to stop it.

I am running Outlook with just POP3s. Not an exchange server.

My O/S is XP Pro SP2 with ZA Security Suite.

I have Googled but nobody seems to have come up with an answer.

Do you have a PDA or something similar pluged into the pc?

Nothing.