I receive an "error signing in message" when I try to access right hand options "Export PDF, Send, etc" I can sign into the Adobe site fine and my membership is paid through May 2019.
We have checked your Adobe account and there's nothing wrong with the service.You still have an active subscription of "Adobe Export PDF".
As mentioned, you have been getting "Sign In" error while clicking "Export PDF" feature available in the right hand side Tool-pane. There could be a possibility that there is some connection issue with the application itself.
You may try the following steps-
Let us know if this still doesn't shows any progress.