Your code is missing a bracket and seems to be incorrect format all together.
Have you tried Write("Q3_Pan[0].Part.Type.Code", "x")?
See also what response you will get if you try using:
WriteCustomString(ByVal tagName As String, ByVal value As String, definedStringLength As Integer)
which in your case would be:
WriteCustomString("Q3_Pan[0].Part.Type.Code", "x", 1)