Warnings are notified with a warning icon which turns to red, located at the top-right of the page. When clicked it displays a dialog containing the warning log as below.
Handling Permission Warnings
Most common permission warnings that are about a field that "cannot be set" deal with incomplete project issue type screens configuration. This happens when the custom field in which Crystal Gantt persists the Gantt related task values are not added to a Project's issue type screens.
Here are the steps to be followed to get resolved in Classic Project and Next-Gen Project.