Registration Problems

[Splinteroid]

Hi, I'm having a bit of difficulty with the forum, when a member registers, once they have validated thier account via e-mail and are linked back to the forum, it immediatly logs them out again and then just will not allow them to log in. It acts as if the members don't exist when I search for them in the admin panel, but then if I try to make a new account with that persons username, it says that member already exists and then links me to thier profile page.

This seems to be the root of the problem although I am not entirely sure:

Database error in vBulletin 2.3.3:

Invalid SQL: SELECT count AS messages FROM privatemessage WHERE userid= AND dateline>1099064842 AND folderid=0
mysql error: 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 'AND dateline>1099064842 AND folderid=0' at line 1

mysql error number: 1064

I also got this error too although I'm rally not sure if its even related but i'll paste it here anyway just incase (I'm new at all this):

Database error in vBulletin 2.3.3:

Invalid SQL: INSERT INTO userfield (userid,field11,field6,field12,field1,field2,field
3,field4,field10) VALUES (,'','','','','','','','')
mysql error: 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 ''','','','','','','','')' at line 1

mysql error number: 1064

Any help would be much appreciated & thanks in advance.