Menu configuration is not being saved

Hello there!
I've a project deadline at the end of this month, so any help with this issue will be greatly appreciated. I'm using seven theme for admin part of the site. Menu configuration is not getting saved on the menu items list page. I tried using both drag and drop and weights drop down menu, but none of those work. I have to go to individual menu items to save the order. The list of menu items is very long and users are planning to add more menu items to it. Could you please help me to resolve this issue? Please let me know if you require more information.
Thanks in advance!