Symptom happens when doing Test Program in Program Editor. Error cursor appears beneath the element name.
Here is a shorter version, same issue:
Radio Group is named OrderType
Options are Purchase Order, Sales Order, Job Order
When PO is selected, then SO and JO should be ReadOnly and/or Invisible so user cannot change after selection.
The sample below is showing four lines that each fail. Would not normally use all four like this, but just trying to show four line that each fail.
IF OrderType = "Purchase Order" THEN {
ReadOnly(rbtnSalesOrder,1)
ReadOnly(OrderType!rbtnSalesOrder,1)
visibility(rbtnSalesOrder,0)
visibility(OrderType!rbtnSalesOrder,0)
}
Code is set when Element Changes and when Form is Entered. Various elements, labels, colors, etc. are changed based on OrderType. This allows selection when record is Added, but does not allow changing. And it also provides proper visual presentation when record is opened in future.
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Subsequent Edit:

Never mind. Problem fixed. Thanks for confirming that feature was available now.
Thanks for forcing me to provide code. The dummy at this end was using the wrong names for the radio buttons in the coding. Actual names were
rbSalesOrder, etc. not
rbtn.....
Carry over from changing my naming conventions.
Aaaargh!