Error each time a new user register

[desmomax]

I moved my database from snitz to vbulletin with the soft provided with vbulletin

but i receive an error report EACH time a new user register to my forum,
the problem is that the forum report an error and the registering procedure stop so i dont receive notification etc..

here is the error:
Database error in vBulletin 3.6.9:


Invalid SQL:
INSERT INTO userfield
(field2, userid)
VALUES
('roccella jonica', 1510);


MySQL Error : Duplicate entry '1510' for key 1
Error Number : 1062
Date : Tuesday, April 8th 2008 @ 12:11:06 PM
Script : http://www.ilbraccoitaliano.net/foru...p?do=addmember
Referrer : http://www.ilbraccoitaliano.net/foru...p?do=addmember
IP Address : 79.3.115.80
Username : cris
Classname : vB_Database_MySQLi



can some one help me?

thanx