The UsersAndRolesTabHandler the error message refers to is from OJS 3.0.x and has been removed in 3.1.x and newer; see e.g. [SOLVED]OJS upgrade 3.0.2 to 3.1 error Users& Roles Pages - #7 by 1116. The most common cause of this is a browser cache, but if you’re seeing this on other browsers/systems as well, then is it possible that there is still OJS 3.0.x code on your server?
Regards,
Alec Smecher
Public Knowledge Project Team