It could be add-ins causing the issue.
Disable/Enable Add-ins in Outlook 2007:

1. In Outlook 2007, go to Tools > Trust Center
2. Click on the Add-ins section
3. You will now see all active, non-active, and disabled add-ins. Click on the add-in you want to enable/disable and then click on the Go button towards the bottom.
4. This will then open up the COM add-ins page. You can then check/uncheck the add-ins you want to enabe or disable.