Menu unserialized warning when using autocomplete in a custom module
There are three functions calling menu_unserialize(), the function for which the error is reported:


menu_get_item() uses it in the following code

  if ($router_item['access']) {
    $router_item['map'] = $map;
    $router_item['page_arguments'] = array_merge(menu_unserialize($router_item['page_arguments'], $map), array_slice($map, $router_item['number_parts']));
    $router_item['theme_arguments'] = array_merge(menu_unserialize($router_item['theme_arguments'], $map), array_slice($map, $router_item['number_parts']));
  }

_menu_check_access() uses it in the following code

$arguments = menu_unserialize($item['access_arguments'], $map);

_menu_item_localize() uses it in the following code

$item['title'] = t($item['title'], menu_unserialize($item['title_arguments'], $map));



The Invalid argument supplied for foreach() error simply means that foreach() is getting a value that is not an array. With the code you are showing, that is happening only for $arguments = menu_unserialize($item['access_arguments'], $map); since you are setting $item['suggest_feature/autocomplete']['access arguments'] to TRUE when it should be an array. 

In your case, the code should be the following one.

/**
 * Implementation of hook_menu()
 */
function suggest_feature_menu() {  
  $item['suggest_feature/autocomplete'] = array(   
    'page callback' =&gt; '_suggest_feature_autocomplete',   
    'access arguments' =&gt; array('access example autocomplete'),
    'type' =&gt; MENU_CALLBACK
  ); 

  return $item;
}


For Drupal that code would be equivalent to the following one.

/**
 * Implementation of hook_menu()
 */
function suggest_feature_menu() {  
  $item['suggest_feature/autocomplete'] = array(   
    'page callback' =&gt; '_suggest_feature_autocomplete',
    'access callback' =&gt; 'user_access',
    'access arguments' =&gt; array('access example autocomplete'),
    'type' =&gt; MENU_CALLBACK
  ); 

  return $item;
}


You can understand now why your code is wrong.

It's not the access arguments that you can set to a boolean value, but the access callback. See what the documentation for hook_menu() says. (Emphasis is mine.)


  
  "access callback": A function returning TRUE if the user has access rights to this menu item, and FALSE if not. It can also be a boolean constant instead of a function, and you can also use numeric values (will be cast to boolean). Defaults to user_access() unless a value is inherited from the parent menu item; only MENU_DEFAULT_LOCAL_TASK items can inherit access callbacks. To use the user_access() default callback, you must specify the permission to check as 'access arguments' (see below).
  


And for the access arguments, it says:


  
  "access arguments": An array of arguments to pass to the access callback function, with path component substitution as described above. If the access callback is inherited (see above), the access arguments will be inherited with it, unless overridden in the child menu item.