Do a project/directory wide search in your theme directory for add_menu_page and make sure second and first parameters of any calls to that function does not supply anything weird. By the looks of instead of a page name, the result of get_bloginfo('stylesheet_url') is used when setting up the menu page.
Also, if possible, try temporarily deactivating all your plugins or switching to different theme to verify that this is in deed caused by your theme, and nothing else.