I have a been using my tablet for a year or so, no problems, and all of a sudden the pattern password will not work, its just like I'm doing the wrong one. So.... you should be able to unlock via the gmail account and passoword. HOWEVER, i have never used my gmail account - I just created one to set-up the Nexus - and this has now been deleted by Google as it was dormant.
So I can't use the pattern and can't use my gmail account.
So how do I unlock my tablet ???