This problem are still unsolved.
Where can I locate _forms/FormScript.js.aspx? so I can physically edit the code that throws the error. I'm no coder, but when I see an error like this I tend to locate it, change it and often it solves the problem.
1. locate _forms/FormScript.js.aspx?
2. Edit line 98 with the missing ")"
3. Publish the change and cross my fingers.
I've talked to another user, and he have not the same issue with the menu ribbon.