Field & of object & is not read only.

What causes this issue?

The field relationship 'S' was specified, but the object field &V1& is
not flagged in the data dictionary as a subset field or read-only field.

System Response

The view cluster was not activated.

How to fix this error?

The specified field dependency is probably for navigation, so the type '
' must be entered in this case.
The following values are valid field relationship types:
' ' : (foreign) key dependency (normal case). The relationship is used
in the navigation and when determining dependent entries.

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

'S': the object field is read only. The value for this field is defined
in the predecessor object, and is only displayed in the current object.
The field is flagged in the data dictionary as a subset field, but it is
not a key field, it is a text field which contains an explanation of a
key field which is defined as a subset.
The field is flagged in the data dictionary as read-only.
If case 2 applies, you must flag the field in the data dictionary as a
subset field or a read-only field.

Error message extract from SAP system. Copyright SAP SE.