I'm guessing that's because you don't allow guests to view the threads in question. Facebook is actually getting an error (probably a no permission page).
That's my guess too. We allow them to see the list of threads but not open threads... Anything I could tweak to get rid of the error but keep our security the same?
I understand that. I don't want the content to preview. I just don't want it to say error instead. If I could literally just remove the word error I'd be happy.
The page is very likely the standard no permission page, so there isn't really a way built into XF to change that for just this case. I believe you could change the "error" template, but that is for every error that can get triggered.