Trouble submitting forum reply

[reboot]

Got this nice message of the cacti forum while posting a reply.
It took me some time to write the reply (5 - 10 minutes or so). When I submitted my post, I got the message below.

So I hit the back button and copied my post into the clipboard. I retried, but got the same error. Then I went back to the topic I wanted to reply on. I replied again, pasted my message and submitted it again. This time it went right.

It's this reply.

=======================================

Error in posting

DEBUG MODE

SQL Error : 1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'WHERE forum_id = 21' at line 3

UPDATE forums SET forum_posts = forum_posts + 1, forum_last_post_id = WHERE forum_id = 21

Line : 423
File : functions_post.php