Fatal Error coning files

I am receiving this error.

Fatal Error: This should not happen but is most often caused by other plugins. Try first the option “Optimizer” in WP Staging->Settings and try again. If this does not help, enable wordpress debug mode to find out which plugin is causing this:
404 Not Found

I have used the Optimizer to switch of all the plugins during coping. I have switched WP staging debug on and get no error.
under the files I have excluded big files “old_site_back” and WP_Snapshot to no avail.
I downloaded and tried the beta version. 2 hrs later it was still resetting memory.

any idea what might be the issue