OG Forum (No forums defined error)

Hi there,

I have a strange problem with my OG forum module (I have installed forum and the og module)
When I add the og_forum module everything works fine at first. Every group gets an own forum and I can access the forums. However, this only works when I am logged in as admin. As soon as I am logged in as a normal user something goes wrong.
When I access the normal forum page, it is blank, and I get the message 'No forums defined', even the not-og-forums are gone. And i get the following php error.

user warning: You have an error in your SQL syntax near 'SELECT x.tid FROM (SELECT ogt.tid FROM og_term ogt INNER JOIN og_uid ogu ON ogt.' at line 1 query: SELECT DISTINCT(t.tid), t.*, parent FROM term_data t INNER JOIN term_hierarchy h ON t.tid = h.tid WHERE (t.language ='en' OR t.language ='' OR t.language IS NULL) AND (t.tid NOT IN (SELECT x.tid FROM (SELECT ogt.tid FROM og_term ogt INNER JOIN og_uid ogu ON ogt.nid = ogu.nid AND ogu.uid != 2) x WHERE x.tid NOT IN (SELECT ogt.tid FROM og_term ogt INNER JOIN og_uid ogu ON ogt.nid = ogu.nid AND ogu.uid = 2)) AND t.tid NOT IN (SELECT ogt.tid FROM og_term ogt INNER JOIN og_uid ogu ON ogt.nid = ogu.nid AND ogu.uid = 2 WHERE ogu.is_active = 0)) AND ( t.vid = 1 ) ORDER BY weight, name in /home/lalala/www/includes/database.mysql.inc on line 172.

As soon as I switch of the OG forum. everything is back again. But in that case everybody is allowed to use the group forums, i.e. they are not any longer under the group constraints.
Why does it work for me as admin but not for the normal user?

Any ideas?
Thanks
Martin