caused customizer errors

Like hubsplash wrote, Piklist caused a customizer display error. This happened immediately after I added a masthead image. Deactivated all plugins and isolated the problem to Piklist. Interestingly, also like hubsplash, I also had to deactivate WP Helpers. WP Helpers was the reason no one could access my site (attempts to do so went straight to the login page on other computers).