I have never seen anything like this on my Mac.
Please provide details: What USB to RS-232 device are you using? Which chipset does it use? Do you have the latest drivers? Which version of OS X and which version of LV and VISA are installed? What is your software doing when the freeze occurs? What program are you using for the serial communications? What device is connected to the port? Do you have any other software which can communicate successfully with the device?
Lynn
