Which notifications you are using?
Without any details it's hard to help why notifications are send twice.
What is triggering the notfications? (When an object is created? When an object is updated?)
What critiera is configured?
Are all notifications sent twice? Or just some or one?
If you check the status of the notification workflows are there two entries in the log? Or just one entry and the notification email is received twice in the mailbox?
Andreas Baumgarten | H&D International Group