I was just about to ask if you had it right 🙂  Here's what it says when i reference the diag number: 

The following diagnostic is generated: e-file: (state) There is an amount on the Federal Form 1120. A copy of the certification must be in the e-file or included as a PDF attachment (ref. #40721)

What needs to be done to clear this diagnostic? A copy of the Federal Form 1120 must be included with the e-file. This can be done by printing the Federal Form 1120 to PDF and attaching in Screen 4.2 Electronic Filing.