Error after plugin install

Hi Alex,

When i installed this plugin, i am getting same errors multiple times in the plugin settings page.

One like below:
Strict Standards: call_user_func_array() expects parameter 1 to be a valid callback, non-static method Virtual_Queue_Admin::theme_options_page() should not be called statically in /home/user/public_html/wp-includes/class-wp-hook.php on line 287

And:
Strict Standards: call_user_func() expects parameter 1 to be a valid callback, non-static method Virtual_Queue_Admin::display_header_options_content() should not be called statically in /home/user/public_html/wp-admin/includes/template.php on line 1688

Could this be because of php version conflict? Thanks.