Prepare Form menu items not working, drag them to document and they won't insert text field or checkbox or whatever, a circle with line draw through it appears.

Prepare Form menu items not working. I drag them to document and they won't insert text field or checkbox or whatever, a circle with line draw through it appears next to the item. It's not question of needing to upgrade since I have Adobe DC Pro and have already created a filable PDF with no problem, the Prepare Form Tool and it's menu working fine initially, now all of a sudden not. Please help.