As explained in the description of the Network Admin Users screen, in a network install (multisite mode) users are
added on a global basis to the entire network, then assigned to specific sites
Normal administrators are not permitted to modify these global profiles, since their privileges extend only to their given site. This task is reserved for super administrators, who have full control across the entire network.
In prior versions of WordPress, when multisite installations relied on separate WordPress MU support, you could define EDIT_ANY_USER to be true in your wp-config.php file. However, since multisite support was natively integrated, I believe that this was removed.
To manage network users from the Network Admin Users screen, a user must belong to a role that has at least the manage_network_users and edit_users permissions. You could try creating a custom role that included these and the standard administrator permissions, but I’m not convinced how effective that would be. Personally, I’d just try to avoid circumventing these restrictions.