RosemaryK on "[Plugin: Wordfence Security] Administrator and comments blocked"

I installed Wordfence recently. My son and I logged in as administrator at the same time (which we have done in the past before installing Wordfence). I went to Settings to change my URL from http://www.bloisdailyphoto.com to http://www.loiredailyphoto.com (both these addresses go through the same server). I clicked save and we were then both asked to log in again but couldn't. Nothing happens. There is no message. The User and Password boxes simply empty.
I tried to comment without logging in and I simply get a blank screen.
Can you tell me how to solve the problem please.

https://wordpress.org/plugins/wordfence/