I'm glad you were able to discover the cause for this. When you see what you are seeing in the screenshot you sent, it means that there is no catalog of teh backup. This can be caused by:
- letting the Protection expire on the Backup session
- Backing up with Protection set to None
The only way to recover from this is to either Export/Import the media, or, as you did, Import the Catalog
This may allow you to restore, but, the Daily Maintenance, which runs at noon each day, will see an uprotected session, and delete teh catalog to save on disk space. After Importing, if you are not totally done with this session, you should set your protection to a higher value, or Permanent, it can be recycled later