Outlook 2007 wouldn't close properly after I updated my Avast 7 Free installation to version 7.0.1426. It would reopen, and after closing it again, a message would appear in the system tray alerting me that Outlook was trying to save my data. I am running Windows 7 Ultimate 32 bit.
I fixed this issue by restarting the computer in safe mode, logging on as the administrator and opening Outlook without email support. I then clicked on the "Tools" menu, then on the "Trust Centre" entry, then on the "Addins" item in the left pane, then on the "Go" button next to the "Com addins" field. Once in there, I unchecked the "Avast Antispam" plugin checkbox, clicked OK, closed Outlook, then restarted the computer in normal mode. I then logged back on as the standard user and tested Outlook again. This solved the problem. Outlook works properly again.