I have this rather peculiar issue with the Admin Settings panel:
I've had SEC working just fine with my site, but I opted to try out the advanced option to use my own CSS. I applied the check mark to that setting and saved. Immediately the SEC Admin Panel disappeared.
My event listings still work, but I cannot figure out how or why this Admin Panel for SEC is gone.
I've tried deactivating/activating and even re-installing the entire plugin. No dice.