I apologize for not catching this request much sooner. You didn't post specific errors, so I'm not able to determine what you may have experienced. However, I did learn that Gatekeeper was conflicting with other plugins and themes (and those plugins and themes, if used together, were most likely conflicting with one another). I've since released a fix to avoid those conflicts (and hope other developers do the same). Gatekeeper shouldn't have locked you out of your admin pages, however. The code was written to specifically avoid interfering with the admin login page, so I'm a bit confused on that one.
I'm sure you have long since resolved your problems (and I apologize again for not seeing this request sooner), but if you do continue to have problems with the plugin, please let me know.