Is it just one file?  Have you tried opening other clients to see if you have access?  Do you have a backup of the client, just in case the file is corrupted and you need to restore it to when it was working?  

I have just encountered the same problem. I am unable to open a client I had just made changes to prior to submitting it for electronic filing but get the same message "unable to read data, restart the program" or words to that effect. My file is probably corrupt as my keyboard froze and I turned the machine off. I do not have a backup of the current year file. I suppose I might have to delete the file for 2019, go back to the 2018 file and transfer it to 2019 again and start over? Any help?

I have been using Pro Series Professional since 2006.  I had this problem a few times the last few years, but none this year.  Unfortunately, there was nothing that could be done.  Which annoyed me greatly.  If someone knows a solution, I'd love to know of it.