Dynamically Assign Parent Incident Contact to Child Incident using workflow

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I am trying to assign the parent incident primary contact to child incident primary contact using workflows. But when I am selecting the Contact value as "Initial contact" or "Last Contact", it's popping up an error "can not find the "last Contact" in the list of available records".

Attached the same error image.  Please check the attached image. 

Can anyone have any idea to solve this issue?