I agree.  This problem is very frustrating.

I've had this issue with one or two customers.  This is what has worked: 

1. Make a backup copy of the existing file then replace with  SY_FormsEfilingVersion.M4T

2. If that doesn't work I've had to edit the SYS record to modify the LastRegistrationDate which I usually take from a working system.

On at least one customer this fix does not seem permanent as they continue to see DEMO mode each year. We now save a copy of this data file and hope that copying/pasting it works.

Always save a backup of any files you edit or copy over BEFORE you make those changes.

Did you try adding the trusted sites referenced in this post?

https://www.sagecity.com/support_communities/sage100_erp/f/sage-100-technical-and-installation-discussions/143547/1099-demo-mode-problem 

I did...and it didn't help.  Sage support sent me a copy of SY_FormsEfilingVersion.M4T, but it didn't help either.  I was able to copy that file from another client's system to fix the problem.  

I can't believe this is still the same resolution from years ago when this issue originally surfaced, i.e. copy in SY_FormsEfilingVersion.M4T from a working system. 

"Always save a backup of any files you edit or copy over BEFORE you make those changes."

This advice can't be repeated enough.