Sandy isn't able to send me a tweet. (changed twitter usernames)

I already went through the twitter verification process a while ago... then later I changed my twitter username. Now when I enter my new username on the /settings/twitter page and click "Test", I get the error:

I wasn't able to send you a tweet. Please double check your Twitter user name and try again.

I'm following 's' on twitter, and 's' is following me. I even tried blocking, unblocking, and re-following now that I have the new username... she still "isn't able to send me a tweet" for some reason.