Login / Access issues getting into wp-admin

I'm having issues getting into the wp-admin section of my site.

I have the branding plugin installed, so in theory when you pop in drgeraldlewis.com/wp-admin you should get the logo plus a login box. At the moment I get a white box popup saying you need to enter the username and password, which it then repeatedly rejects (even when the information in correct). It then brings up the message "Authentication Required".

I am currently using chrome, but out of curiousity I tried another browser I use, Epic. When I try to login from here, I get another white popup box where it asks me to enter a preset username and a maths question's answer as the password. If you do this correctly it lets you get to the wp-admin login box.

Can someone please help me fix this - my members / users can't log into the site (I'm getting complaints), and suggesting the Epic 'workaround' isn't really a reasonable solution. I have included a file that has both the different screenshots I've been getting.

Any help would be much appreciated :slight_smile:

Thanks!