I've looked into this, and I think I know what happened. We have various systems in place to monitor the site for suspicious behaviour (spam, etc.) It looks you inadvertently got caught up in some of these filters, even though you're obviously not doing anything wrong.
We've adjusted the parameters of these filters to prevent this from happening again. Please wait at least 24 hours for the filters to refresh, and then try returning to your usual workflow. As usual, if you experience problems again, please contact us.
We are very sorry for the inconvenience, and appreciate your patience!