I think you are right for IDN command. It does initiate SYNTAX ERROR.
I did use NI Spy application and find out that there are more different issues going on.
Here is the message about error that I got:
134. viRead (VXI0::2::INSTR (0x00FAE318), "INVALID TRI-STATE COMMAND 'R'..", 1024 (0x400), 31 (0x1F))
Process ID: 0x00000D3C Thread ID: 0x00000F1C
Start Time: 14:39:33.4130 Call Duration 00:00:00.0100
Status: 0 (VI_SUCCESS)
