To delete the discussion directly without entering it use command code 42. Logon as sysop but don't access the problem area. In your browser modify the URL while maintaining the user certificate (the random characters between the "@" signs):
Note the change to command code 42 and the Web Crossing ID for the particular discussion where the problem exists.
The same technique is used to delete a folder (use command code 40 instead of 42, a link (use command code 140 instead of 42), or a chat (use command code 195 instead of 42) or a message (use command code 64 instead of 42)
You may also click the EXPORT button in the containing folder, then choose the MOVE, EXPORT OR DELETE option. Select the errant item, and then delete it (not for individual messages).
If this technique doesn't solve the problem, move to the folder containing this discussion or folder and export everything but the problem area. Delete the folder (which will delete the problem discussion), then recreate it and import the items you exported.