I don't think downgrading PHP will help much as my online WP install uses PHP 5.3.2-1ubuntu4.20 and has the same error. I do use WP 3.6 on both servers.

I changed the error reporting in my php.ini to: error_reporting = E_ALL & ~E_STRICT
This didn't help me, still get the same error 

Edit:
Downgraded WP to 3.5.2 but that didn't help either.

I am having the same issue, a white screen when activating the theme. This happens on my localhost but also at my online WP install.

I have installed a fresh WP 3.6 and are running PHP Version 5.4.9-4ubuntu2.2

Anyone have ideas how to solve this?

Strict Standards: Declaration of nav_walker_description::start_el() should be compatible with Walker::start_el(&$output, $object, $depth = 0, $args = Array, $current_object_id = 0) in /home/jan/public_html/wp-content/themes/symbiostock-a640bd8b08175dba50c6a69314904d2ed0379860/inc/classes/nav_walker_description.php on line 92

Strict Standards: Declaration of nav_walker_mobile::start_lvl() should be compatible with Walker::start_lvl(&$output, $depth = 0, $args = Array) in /home/jan/public_html/wp-content/themes/symbiostock-a640bd8b08175dba50c6a69314904d2ed0379860/inc/classes/nav_walker_mobile.php on line 61

Strict Standards: Declaration of nav_walker_mobile::end_lvl() should be compatible with Walker::end_lvl(&$output, $depth = 0, $args = Array) in /home/jan/public_html/wp-content/themes/symbiostock-a640bd8b08175dba50c6a69314904d2ed0379860/inc/classes/nav_walker_mobile.php on line 61

Strict Standards: Declaration of nav_walker_mobile::start_el() should be compatible with Walker::start_el(&$output, $object, $depth = 0, $args = Array, $current_object_id = 0) in /home/jan/public_html/wp-content/themes/symbiostock-a640bd8b08175dba50c6a69314904d2ed0379860/inc/classes/nav_walker_mobile.php on line 61

Strict Standards: Declaration of nav_walker_mobile::end_el() should be compatible with Walker::end_el(&$output, $object, $depth = 0, $args = Array) in /home/jan/public_html/wp-content/themes/symbiostock-a640bd8b08175dba50c6a69314904d2ed0379860/inc/classes/nav_walker_mobile.php on line 61

Warning: require_once(/home/jan/public_html/wp-content/themes/symbiostock/inc/classes/network-manager//network-manager.php): failed to open stream: No such file or directory in /home/jan/public_html/wp-content/themes/symbiostock-a640bd8b08175dba50c6a69314904d2ed0379860/functions.php on line 730

Fatal error: require_once(): Failed opening required '/home/jan/public_html/wp-content/themes/symbiostock/inc/classes/network-manager//network-manager.php' (include_path='.:/usr/share/php:/usr/share/pear') in /home/jan/public_html/wp-content/themes/symbiostock-a640bd8b08175dba50c6a69314904d2ed0379860/functions.php on line 730