Database error while making post - PLEASE HELP

[XYZ500]

I am getting a database error on my forum whenever any user (including admins) try to make a post. Surfing the forum seems to be fine, but whenever a user tries to make a post, this error appears and this is not letting anyone make a post.

Here is the screenshot of the error. Just blacked out the website URL and IP.



Following is error that is shown in that yellowish box. In the brackets I have written what is shown there, also made that text bold.

Database error in vBulletin 4.2.2:

Invalid SQL:
INSERT INTO bocetapost
(showsignature, allowsmilie, htmlstate, username, userid, title, pagetext, iconid, visible, dateline, ipaddress, attach, threadid)
VALUES
(1, 1, 'on_nl2br', '(forum username trying to post)', 26828, '(thread title)', '(post content)', 0, 1, 1416614576, '39.32.208.108', 0, 165544);

MySQL Error : Duplicate entry '1133455' for key 'PRIMARY'
Error Number : 1062
Request Date : Friday, November 21st 2014 @ 06:02:56 PM
Error Date : Friday, November 21st 2014 @ 06:02:56 PM
Script : http://domain.com/newthread.php?do=postthread&f=89
Referrer : http://domain.com/newthread.php?do=newthread&f=89
IP Address : 39.32.xxx.xxx
Username : (forum username trying to post)
Classname : vB_Database
MySQL Version : 5.1.69

PLEASE TELL ME HOW TO FIX THIS ERROR ASAP.