Data Base error when creating new user!!

[pityocamptes]

Not sure what is going on. I get this message after creating a user or when a user is registering. However, the registration actually goes through if you check users in admincp. How can I fix this?

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Database error in vBulletin 4.2.1:

Invalid SQL:
INSERT INTO userfield
(field1, field2, field3, field4, userid)
VALUES
('', '', '', '', 138);

MySQL Error : Duplicate entry '138' for key 1
Error Number : 1062
Request Date : Sunday, September 22nd 2013 @ 07:48:45 PM
Error Date : Sunday, September 22nd 2013 @ 07:48:46 PM
Script : XXXXXXXXXXXXXXXX/user.php?do=update
Referrer : XXXXXXXXXXXXXXXXXXXXX/user.php?do=add
IP Address : XXXXXXXXXXXXXXXXXX
Username : XXXXXXXXXXXXXXXX
Classname : vB_Database
MySQL Version : 5.0.96-log
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