sounds like there is something left in the receive buffer when you`ll send the new command...
You could try to use the "flush I/O Buffer" VI each time before sending a new command and then wait until all 9
bytes of the answer has been received.
This is how I do this for the GGP command:
You may try to "reprogram" this structure for LABVIEW 7.1 and check if it will work since I`m not able to provide the VI`s in Labview 7.1...