Cannot send iMessages in Mnt Lion

Hey there everyone;

So, randomly, all of a sudden, I can no longer send iMessages from my MacBook.

0. I don't get any error message or warning or even a red ⚠ — when I try to send a iMessage from the Messages app, nothing happens. My typed message doesn't show up, the message doesn't go through, no error.

1. I can send iMessages from my other Apple Devices (iPad, iPhone.) This problem only affects my 10.8.2 MacBook Pro

2. Other protocols work fine—i.e., I can message on gChat, etc. It's only iMessages that's afffected.

3. When I switch user accounts on my Mac, I can send iMessages; this seems to be a limited to my user account

4. I have tried deleting some of the plists, killing imagent and some other items, but it makes no difference. Ran 10.8.2 combo update; deleted my iCloud account from my Mac and my iMessages account from Messsages, logged out of iCloud on all my devices, logged back in. Nothing.

5. Have tried resetting pram, no change.

I think this might have something to do with a keychain error as I believe I was having some keychain difficulties a few weeks ago… but not necesarily coincident with this problem.

Any help or further suggestions would be most helpful!