Notice: Array to string conversion in module_hook()

$hook_info[$hook]['group'] is expected to be a string, as described in hook_hook_info().

group: A string defining the group to which the hook belongs. The module system will determine whether a file with the name $module.$group.inc exists, and automatically load it when required.

$hook_info[$hook]['group'] can be an array only when two modules have a similar hook_hook_info() implementation.

function my_custom_module_hook_info() {
  $hooks['token_info'] = array(
    'group' => 'token.info',
  );

  return $hooks;
}

function mymodule_hook_info() {
  $hooks['token_info'] = array(
    'group' => 'token_info',
  );

  return $hooks;
}