I'm currently using the Altitude Theme from StudioPress. If you're using more than one menu, perhaps a Primary, Secondary and perhaps even a Footer menu, then choosing the option within the MM General Settings / Other Options then selecting the Show Login/Logout Link - it won't work either. The MM code used to display the login and logout links at the end of your menu, interfere with mobile responsive themes.
(Eric please have a look at this ASAP)
The solution is to use this code below. You'll need to open the functions.php file for the Genesis theme you're using and add this to the bottom of your file. Make sure to flush your browser's cache before testing.
If you happened to change the name of your Core login page to something other than "login", then edit the code above to reflect the name of your login page accordingly.
I hope this helps someone. Eric, please fix the login / logout issue as having a membership site is useless if you can't login and most all sites are moving toward mobile responsive theme often with multiple menus.
Also, please remove that out dated Plugin as a recommendation from this page: