Archie, or somebody else, will probably have a better understanding of your code and possible cause for the exception.
For now, I would suggest that you try to catch that exception in a Try/Catch and display it, similar to this:
Try
Dim MyValues0() As String = EthernetIPforCLXCom1.Read("look_doser_sn_pn_array[0]", 999)
Dim MyValues8 As String = EthernetIPforCLXCom1.Read("MDY10")
Catch ex As Exception
System.Windows.Forms.MessageBox.Show(ex.ToString)
End Try
This might provide more info for the exception itself.
Breakpoints at the above two "Dim" lines would also work.
Could also place a BasicLabel on the form and set its PLCAddressValue to MDY10 and comment out the above two "Dim" lines.