You're about the 4th person I've heard of who's run into this.
Prior cases I'm aware of were handled by our care specialists. I believe it's taken a series of trial and error with folder permission and users.
Here's some examples of fixes that were reported. My hope is that these will provide you with the spark of an idea of what to try. I'll also point out your post and they'll reach out.. i'm just not sure what their backlog is and when they'll be able to call. You can also try calling our frontline agents.
Case #1 The Windows "Users" group did not have full control permissions on the ProWin20 folder. Changing that and restarting ProSeries worked for this customer with that error message we just talked about.
Case #2: If his IT person would login to his machine with his user profile everything works. He showed me where the IT send an E-file yesterday with no issues. I talked to the customers IT and let him know that if his end users did not have full admin rights to Proseries that the program would not operate as designed.
This year I also got the message and was unable to file returns. I worked with Intuit three separate times and they asked me to get IT help since they did not know how to fix. Last year, I hovered over the ProSeries icon and clicked run as administrator. This year Intuit told me not to do that. Well I did it and presto - my returns can be filed! See if that works.