PDOException: SQLSTATE[23000] when turning on after safe rule

Here is what I'm doing: I have a node A with a node reference to node x. A rule sends me an email when a node A is created.
If I turn off the rule, the error does not occur. If I leave the node reference blank, the error also doesn't occur. The mistake must be somewhere in the combination of these two modules. It seems not to have an impact whether I give access to anonymous user or only to other roles.

PDOException: SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry '379-0-all' for key 'PRIMARY': INSERT INTO {node_access} (nid, realm, gid, grant_view, grant_update, grant_delete) VALUES (:db_insert_placeholder_0, :db_insert_placeholder_1, :db_insert_placeholder_2, :db_insert_placeholder_3, :db_insert_placeholder_4, :db_insert_placeholder_5); Array ( [:db_insert_placeholder_0] => 379 [:db_insert_placeholder_1] => all [:db_insert_placeholder_2] => 0 [:db_insert_placeholder_3] => 1 [:db_insert_placeholder_4] => 0 [:db_insert_placeholder_5] => 0 ) in node_access_write_grants() (line 3440 of /home/httpd/vhosts/eeschweiz.ch/httpdocs/modules/node/node.module).

Weird is: If I use "Before Content is Saved", everything works fine. Thats why I think it is a rules problem.