Workmail reports: You are currently not allowed to send this e-mail.

One of my addresses is trying to send about 190 email and they are getting the error "You are currently not allowed to send this e-mail" for all the emails. I am sure that is well below the sending quota. What could be the problem. The dashboard does not show anything that would indicate why this is the case. We are sending using a custom domain and now the awsapps.com account. What could be the problem?