A couple of weeks ago, I explained how to fix a corrupt menu where a separator item could not be added.
One thing I forgot to mention in that post is that clearing down the Menu Master, which is then rebuilt when logging into Dynamics GP again, is that this cleardown will speed up the logging in process as GP will have fewer entries which it needs to check your user has access to. This is something we schedule in whenever we are doing an upgrade (or if users off off for a Reconcile or Check Links to be run).