Cannot sign into iMessage in Mavericks

Hello all,

Writing this from my new rMBP with Mavericks which I'm enjoying very much. One issue keeps bugging me though.

I cannot sign into iMessage. It keeps giving me the error "could not sign into iMessage. Check your connection and try again."

iMessage works perfectly fine on my iPhone and iPad with the same credentials, so I'm not sure what's going on. I've changed the password and that didn't help. And for what it's worth, my previous MBP that I upgraded from Mountain Lion to Mavericks worked until I signed out of my iMessage account and tried to sign back in.

Anyone else having trouble with Messages (specifically iMessage) on Mavericks?