Debug Login Not Working

WP Super Cache isn’t working on our server at all, on any sites, all of a sudden. I’m working with one site in particular and it will not allow me to access the Debug log file. I get the login popup window, but entering the user\pass simply reloads the page. I’ve even looked in the actual .php file in the /cache/ folder and have taken the user/pass directly out of it…same thing.

Thoughts?