Hello,
This looks similar to the issue discussed here: : Validation error from outdated files in sys/versions (regression?)
Unfortunately, there is currently no solution available to launch a session. I hope it gets fixed soon!
In your UEFN project, what is the number of the latest version shown in the project size window?
In my case, the version number there is higher than the one generated in the sys folder. I was thinking that might be the issue.