Bonxy

try the usual way. Like I said, at application startup, do the openserialport method call(without the using keyword). Then when you are about to close the app, close serial port(dont know if theres a method for this). I wouldnt mind giving it a shot, but it will take a couple of days since I am very tied up right now with other assignments.
Perhaps you could ZIP attach the app for me to look at.

Jerson