I don't think LabVIEW echo's characters, I suspect that it is on the remote device that you need to turn off the echo. If the remote device echos you get a copy on the PC of everything sent (Actually this is good for ensuring reliable communication).
I suspect that you need to check the manual for the remote device.
I am one device of 8 communicating with a two wire current loop system. I am inserting my device into the current loop with a current loop to 232 converter. Because all communications is contained within the loop anything i send on the loop i will receive on the loop even with the 232 converter. I need to suppress any echoes due to transmiting
If the data is being sent around the loop then this is a good error check, you just need to flush it from the received input data stream. If using VISA you can clear the input buffer using a VISA function (its in the Interface specific pallette) or filter the duplicated characters as needed by ignoring the character as its received, by comparing the character with what was sent (this would be the error check).
I guess that it's a master slave arangement so the remote devices are responding to commands from a controller, the P.C.)