It seems the code to fix this isn't perfectly effective. <img src="https://www.ubbcentral.com/boards/images/graemlins/frown.gif" alt="" />

You can delete and enter the threads from other threads - enter a thread directly above or below one of the subject-less ones, then use the Next or Last links within.

I believe prune by user is reliant on the search Index. You might try rebuilding the search index, then trying the prune again.

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Charles Capps, Moderator, Post-Install Troubleshooting
PLEASE NOTE: Due to time limitations, I do not provide UBB support via email.