If you are viewing them from the admin menu - using the "viewexpthreads.php" script they will be ordered by the date posted and not reply.
Backup your script first - and try this:
Open /admin/viewexpthreads.php in a text editor.
## Change this:
ORDER BY t1.B_Posted DESC
## To this:
ORDER BY t1.B_Last_Post DESC
that should do the trick - sorting by the last post to the thread. If they seem "upside down" you can do this instead:
ORDER BY t1.B_Last_Post ASC
