Warning when switching theme by Theme Switcher

When switching theme by Theme Switcher, the following warning occurs.

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 'WHERE uid = 1' at line 3 query: UPDATE xmlsitemap_user SET
pid = NULL, last_changed = 1194784959, previously_changed =
last_changed, priority_override = WHERE uid = 1 in
/virtual/****/public_html/includes/database.mysql.inc on line 172.

Thanks in advance.