Creating menu always gives error A name is required for this term

Question

I have 2 menus.

1. Main Navigation
2. Footer Navigation

And 3 locations:

1. Top Bar Navigation
2. Main Navigation
3. Footer Navigation

If I try to create a new menu, wp displays error

A name is required for this term.

Obviously I am giving a name in Menu Name textbox... Is this a bug?
Is there a limit to WP menus?
How can I go about adding another menu to use on an existing page as submenu within the page itself?
Thanx

EDIT 1
Do I need to add:

function register_shop_submenu() {
  register_nav_menu('shop-submenu',__( 'Shop Sub Menu' ));
}
add_action( 'init', 'register_shop_submenu' );

to functions.php?
Is that it??
The admin button option exists in vain??

EDIT 2
The code above just added a new location.
While Manage Locations tab on admin panel now displays:

Your theme supports 4 menus. Select which menu appears in each location.

Clicking the use new menu next to the drop-down of this new location yields same error....
rrrrrrrrrrrrrrr

Answer 1

I got the same issue and found that the plugin user-activity-log was at the origin of the problem.

As I reported here,the problem is related to the hooks:

• ual_shook_created_term
• ual_shook_edited_term
• ual_shook_delete_term

They return nothing instead of the given term when the taxonomy is ‘nav_menu’.

If you don't use this plugin, check the others plugins that call for example the pre_insert_term filter. They should return something.

Answer 2

In my case, it was related to qTranslateX plugin. Just select default language in your Admin Panel, it would save normally. If you will select non-default - you will get same error 'A name is required for this term.'