Editing disabled for one field

[FM5091]

Hello, I have feature layer that had editing enabled for all fields. I am now getting this error in the form.

Here are the settings for the field.

Any Idea how or why this happened? 

[Teresa_Blader]

I see this for my relationship key fields for the related layers, and am currently trying to navigate this as well. Not sure what causes it or where it comes from.