From Liz S, data curator:

I attempted to give user group permissions to Stanley and I got the following error three times in two different browsers, "Our apologies, an error has occurred that we were unable to recover from. The problem has been logged and the administrator notified". Is something wrong with the registration process or are there updates going on with the ESG? I will wait until tomorrow morning to try again and to repond to Stanley Glidden.

Looks to be an issue w/ ContactBuilder and event listener.
Note, that checking one or more permissions causes ISE.

Further review shows a contact is created when user is added to group. An exception may be thrown when users with null middle name are generated via a configured event listener.