'Public Function DisplayCellFunction(cellID1 As String, cellID2 As String)
Public Function DisplayCellFunction(cellID1 As Integer, cellID2 As Integer)
'Copy formulas to the adjacent cell for visual verification
'Range(cellID1) = "'" & Range(cellID2).Formula
Range("F26") = "'" & Range("d26").Formula
End Function


In the workbook I enter

=DisplayCellFunction(F26, D26)
I get a #Name Error

=DisplayCellFunction("F26", "D26")
I get a #Name Error

=DisplayCellFunction(6, 6)
I get a #Value! Error