Unable to edit post categories in the single entry view

Hi there,

I am trying to add a form to add new clients to our agency database. So I have fields: Name, company, address, etc, and among them I want to have: “Client type” with the posts categories dropdown (for example: “web”, “video production”, etc). However, when I click on the “category” field in the “post fields” menu, i get a javascript popup saying “The page at localhost says: 0” (not sure why that’s happening), and then proceeds to create a Category field. Once I have all my categories in, I am trying to edit the entry through the single entry view, and that’s where I am having problems:

1. The single entry view doesn’t remember which categories were already selected (so I have to recheck them again)
2. The form won’t let me save changes, I get this error:

“There were errors with the edit you made.

Post Category: Invalid selection. Please select one of the available choices.”

Where am I going wrong?

Thanks,
Yulia.

https://www.ads-software.com/extend/plugins/gravity-forms-addons/