JS error on every theme -Uncaught ReferenceError: jQuery is not defined

Hi, again
On every theme I tried, I got the following javascript errors when I look the page with chrome (and enabled "inspect element")

Uncaught ReferenceError: jQuery is not defined     dropmenu.js:2
Failed to load resource: the server responded with a status of 404 (Not Found)  ..../wp-content/themes/black-letterhead/none

I'm pretty sure the problem is on the functions.php file of each theme and more specific at the add_wp_menu_drop_js_script()function , which is in all themes the same and doesn't use the enqueue_script. But I don't know how to fix it.

Can someone help?
I use WP mulisite 3.5.1 , BP1.6.5 and the only plugins I have enabled so far are
BP Groupblog, BuddyPress, BuddyPress Group Calendar, Sidebar Login widget

Thanks in advance
Lena