iMessage not longer working

I can no longer send or receive messages on my iPad associated with my apple.id

I've turned if off and on, restarted iPad, changed apple id's but still keep getting "not delivered" in red text.
It gets to about 95% completed but just hangs there.
My phone's iMessage works fine but it's not associated with any apple id, just my number.

Not sure if it's got anything to do with my install of Lion at all?

It's the new iPad and latest software.
I've tried sending to phones, iPads and still nothing.

Any tips?

Is the apple ID in use for iMessage (perhaps for example the iMessage Beta on your Mac) on another device?

What happens if you associate iMessage with a completely different email address (maybe even create a GMail account or something to test this)?

This could be wrong info, but mine stopped working on Lion also. Was told the Beta has expired and no longer works when messaging phones or tablets since Mountain Lion is coming out this month. Made sense to me.

http://www.macrumors.com/2012/02/17/after-beta-messages-will-be-exclusive-to-os-x-mountain-lion/