Error in Sale invoice form

Hi, everyone ,I getting an error of VM8761:343 Uncaught TypeError: Cannot read property 'extend' of undefined,
when I am routing to Sale invoice from any another form or trying to create a fresh sale invoice form.
The output of this error is :

Please suggest some solution
Baljeet Singh

Did you do any customization? And are you on the latest version?

Yes, I have add some custom fields in sale invoice form.
But its work previously with out any error.
still its work in between but getting this error most of the time.