When you tested the device and got data, did you do this with the terminal or with the program you wrote? If it was with the terminal, I suspect that in your program you have to add a termination character to the string that you write. This is typically either a line feed or carriage return. These constants are on the string palette. If you tested the device with the first program you wrote, was this written in an earlier version of LabVIEW or something else?
The Open Serial Driver.vi is a VISA implementation of an old driver in which Com1 was mapped to port 0, Com2 was port 1, etc. That may be the cause of your error message. If you continue to have problems, could you also post the VI that you've written?
