Recently when trying to customise a list form with “Customize Form” I came across the following error:
The trick to resolving this was the message “Customizing the form for this content type is not supported”. I was using a content type on the list which was pushed down from a centralised content type hub.
- List settings
- Select the custom content type you have attached
- Advanced settings
- Set “Should this content type be read only” to No
Now you should be able to edit the list form(s) in InfoPath.