My balance sheet, income, and retained earnings all reconcile. On Schedule M-1 there are two entries under 3b, the first is non-deductible travel/entertainment (get that) and the second amount does not have a description. I'm presented with a prompt to enter a description in a box - I do so and it creates a new line with no number. Nothing I do fixes it - so I have a line with a description and no amount, then a line with no description and an amount. What was first defined as one error by error check is now two. I'm unable to get past this and file.
Despite 3 hours on the phone with TurboTax support not resulting in finding a solution, further experimentation on forms resulted in my being able to find an entry point for this necessary information and completion of the error checking process. This is clearly a bug in the program and wasted a ton of my time.
To get around the limitation of the step-by-step process, change to Forms (upper right of program window). Go to "Sch M-1 Wks" and look for the number without a description; here it will allow you to make an entry, and the exclamation point next to Form 1120S p. 3-5 will disappear. You can now complete error checking and file electronically - until I reached this point it was not apparent whether or not I could do that, and Intuit support suggested that I might need to print and file by mail.