Drupal error after creating new theme ,Undefined variable: hide_site_name and other similar error
It looks like you copied the Bartik theme and put inside your "mytheme". 
Do you create new theme or just create theme base on the Bartik theme?
If you want to create the subtheme base on Bartik theme. Please add the default regions in your new mytheme.info like from link : Problems creating Bartik sub-theme

You may also check the tutorial from How to Customize Bartik. It's the nice tutorial for creating subtheme base on Bartik theme.