DB errors when adding to child site

i get the following errors when adding a user to a child site
[code]
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 ''. OG_SITES_HUB_PREFIX .'og_uid WHERE nid = 0 AND uid = 7' at line 1 query: SELECT COUNT(*) FROM '. OG_SITES_HUB_PREFIX .'og_uid WHERE nid = 0 AND uid = 7 in /var/www/web17/web/includes/database.mysql.inc on line 172.
warning: Invalid argument supplied for foreach() in /var/www/web17/web/modules/node/node.module on line 504.
warning: implode() [function.implode]: Bad arguments. in /var/www/web17/web/modules/node/node.module on line 508.
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 n.nid, n.vid, n.type, n.status, n.created, n.changed, n.comment, n.promote, n.sticky, r.timestamp AS revision_timestamp, r.title, r.body, r.teaser, r.log, r.format, u.uid, u.name, u.picture, u.data FROM hub_node n INNER JOIN hub_users u ON u.uid = n.uid INNER JOIN hub_node_revisions r ON r.vid = n.vid WHERE in /var/www/web17/web/includes/database.mysql.inc on line 172.
[/code]

any ideas?