It is happening when I am trying to make changes to my WP menus. I can make the changes, but when I hit save I get either the 404 or 500 error. When I go back to the menu, the changes haven't been saved.
To answer your questions:
1. WP version 3.9.1
2. Shareaholic version 7.4.0.6
3. Clear Line Theme
4. http://runningatdisney.com