The aq agent mapped to more than one database user in the the same session
Map the aq agent to only one database user Check the aq$internet_users view for database users that map to this agent
Browse all solutions to database errors from Oracle, MS SQL or MySQL
Try the following links for this error:
http://docs.oracle.com/cd/E16655_01/server.121/e26079/aqxmlmessages.htm