Sometimes the queue in Project Server 2007 appears to be getting hung up and you find that jobs are not completing successfully from Project Professional. The first steps to take are:
1. Click “Server Settings”
2. Click “Manage Queue”
3. Expand the “Advanced Options” section and ensure that the “Cancel jobs getting enqueued” option is checked.
4. Check the box next to the task you want to cancel and click the “Cancel Jobs” button.
If this still doesnt appear to help then you should:
1. Launch Services
2. Stop the Project Queue Service
3. Stop the SharePoint Timer Service
4. Start the SharePoint Timer Service
5. Start the Project Queue Service