Thank heavens I found this! I came here because I couldn’t get into my backend with my custom slug anymore. It would only redirect.
I wasn’t sure if it was an iThemes update because it worked fine before I was on holiday… and all I did when I came back was update my hosting’s PHP to a newer version. (5.2 to 5.4)
I did all the steps in the first post in this thread, but only finally deleting the Better WordPress Security folder in my plugin directory allowed me to access my wp-admin again. I won’t be installing iThemes again anytime soon!