Submit error related to user.module

On submission of a fairly simple webform I am getting:

* warning: array_keys() [function.array-keys]: The first argument should be an array in /home/mysite/modules/user/user.module on line 378.
* warning: array_fill() [function.array-fill]: Number of elements must be positive in /home/mysite/modules/user/user.module on line 379.
* warning: implode() [function.implode]: Invalid arguments passed in /home/mysite/modules/user/user.module on line 379.
* user warning: 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 query: SELECT DISTINCT(p.perm) FROM role r INNER JOIN permission p ON p.rid = r.rid WHERE r.rid IN () in /home/mysite/includes/database.mysql.inc on line 172.
I did have phplist installed, but removed it and reset settings.php to stock standard just in case it was related.
But same error occurs.
I have browsed the issues for hours and found nothing that matches.
PHP 5.2.6/Mysql 5/Apache 2.
Any ideas?