After upgrading from Nintex 2010 to 2013, I was not able to open the Task form using Nintex Forms, but it popped up and then did not open the Nintex Forms designer. I had tried fixing it by Reactivating the Nintex forms for Workflow feature as explained in the below article
Problem: "Edit with Nintex Forms" does not load Forms designer
Now when I could not open the Insert Reference link to add Custom Javascript in Nintex Task form settings. It does not work and I am not able to add any references.
Does anybody have a solution for this ?