Error on WP 3.9.3

I just installed Nested pages on old WP install, And I got this error when tried to activate plugin.

Site is broken now, please assist.

Fatal error: Call to undefined function NestedPages\Entities\User\wp_roles() in C:\wamp\www\mysite\wp-content\plugins\wp-nested-pages\app\Entities\User\UserCapabilities.php on line 30

{main}( ) …\index.php:0
2 0.0010 204440 require_once( ‘C:\wamp\www\mysite\wp-admin\admin.php’ ) …\index.php:10
3 0.0013 215064 require_once( ‘C:\wamp\www\mysite\wp-load.php’ ) …\admin.php:30
4 0.0015 223056 require_once( ‘C:\wamp\www\mysite\wp-config.php’ ) …\wp-load.php:29
5 0.0019 284672 require_once( ‘C:\wamp\www\mysite\wp-settings.php’ ) …\wp-config.php:92
6 0.6095 32661568 do_action( ) …\wp-settings.php:352
7 1.4856 33949680 call_user_func_array:{C:\wamp\www\mysite\wp-includes\plugin.php:470} ( ) …\plugin.php:470
8 1.4856 33949776 NestedPages\Entities\User\UserCapabilities->addSortingCapabilities( ) …\plugin.php:470