The Maryland Form 511 is currently available for e-filing.  The red "DO NOT FILE" at the top of the form in the software is intended to warn the user that the form is not available to be printed and mailed at this time.  Proseries is currently working with Maryland to secure the necessary approvals on the printed version of the form.  

For example - if you run a print preview of the Form 511, the user will see a watermark on the form stating, "DO NOT FILE" and "E-FILE ONLY".   See picture below.  

Please let us know if you continue to have difficulty e-filing the Form 511.