I just recently upgraded our forum to the latest version. I am getting reports of users not being able to log in after registering and when I go to the members tap in the admincp and click the Members icon I get the message "A configuration Error or Server Error Has Occurred. ! EX0 Something went wrong. Please try again."

Any suggestions?

Is there any type of backend maintenance or diagnostic that can be run via the admincp to verify the forum is working properly? If something is broken, should I re-run the upgrade script?

yes. go to system/support and run the support tools .

it will clear caches and look for issues for you .

if it all fails u can open a ticket aswell