dnb, do you have AIM protocol enabled?
it seems driver or vemstune gets a bit dizzy about this stream of data coming before the port is opened the first time
If you have AIM enabled, try to connect with any terminal program and send "A", then, without restarting ecu try to connect with vemstune again
Once connected, try disable AIM and try to connect to a restarted ecu again
I can reproduce this behaviour here with prolific cable and fw 1.1.63 with AIM enabled
works every time with AIM disabled
//Emil