Thank you for your post.
It's difficult to determine what is the cause without seeing the file. Therefore, you may want to consider renaming your existing Bento database file from bento.bentodb to damaged.bentodb. Launch Bento, and a new bento.bentodb will be created. Then, pull down the File menu and select "Restore from Bento Backup...". Select your last weekly backup file.
If you need the data since your last backup, then feel free to send in your damaged bento.bentodb file and I'll take a look at it. I have sent you a private message with instructions where to send the file.