Add Menu Item Returns: "You must specify a path."

I'm assuming you went to admin/menu and clicked "add menu item". Rather than using the menu_otf feature.

What path did you enter?

I can't reproduce this problem and a quick code audit reveals no obvious errors.

I can't see how that can happen.

You click "add menu item".
menu_edit_item() is called-back
$mid == 0 so menu_edit_item_form is called with

$edit = array (
  'mid' => 0,
  'pid' => 1,
  'type' => MENU_VISIBLE_IN_TREE | MENU_VISIBLE_IN_BREADCRUMB | MENU_CREATED_BY_ADMIN | MENU_MODIFIABLE_BY_ADMIN,
)

$edit['pid'] != 0 so the else is executed
$edit['type'] & MENU_CREATED_BY_ADMIN is true so the form item is created with:

$form['path'] = array('#type' => 'textfield', 
'#title' => t('Path'), 
'#default_value' => $edit['path'], 
'#description' => $path_description, 
'#required' => TRUE);

Can you post your menu.module (or email it to me)?

Are you running any other modules that might interfere with this?