MyBB Community Forums

Threads aren't opening to the right URL causing a 404 error.
Currently they're sending the user to:
http://domainname.tld/forums/thread-{tid}.html
whereas they're supposed to be sending them to:
http://domainname.tld/forums/showthread.php?tid={tid}
I've went from 1.6.5 -> 1.6.10, and I don't know how to fix this error.
Any help would be greatly appreciated.
Same things happens when trying to open categories.
Tries to open to:
http://domain.tld/forum/forum-{fid}.html
should be:
http://domain.tld/forum/forumdisplay.php?fid={fid}

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I've attempted to run /install/ to no avail. Any help guys?

Are you using SEF urls? Also, try to delete your .htaccess and check if it removes the error.