Strange, other than reinstalling OmniData/Scan, I currently don't have any other ideas.
1. Custom scans are automatically backed up, but you can make a manual backup to make sure. Just right-click any OmniScan list while inside OmniScan & select List Maintenance.
2. Uninstall OmniScan/OmniData from your Programs list in the Control Panel.
3. Download the latest install from here. It was just updated recently.
4. Open OT & it will prompt to restore your scans, or you can manually restore them later using the List Maintenance function.
5. Run your ToDo List.