This normally shouldn’t happen, but I suspect the database file may be corrupted.
To clean up the entire newsreader section, please follow these steps:
1) Close Usenapp.
2) Open Finder.
3) In Finder, press Shift + Command + G (or use the menu: Go → Go to Folder).
4) In the text field, enter the following path, including the tilde (~) and click Go:
~/Library/Application Support/Usenapp/articles
5) Make sure you are in the correct folder, then do the following:
6) Delete the file subscriptions.db and remove all folders except the folders named “1” and “2”.
7) Restart Usenapp.
That should resolve the issue.