Hi @cishie,
welcome to the board and sorry for me not replying earlier, eastern kept me busy.
I suspect the error message to originate from the fact that you try to access the Windows COM port with two applications, and PLX DAQ just can get read access to it. By any chance, do you have the Serial Monitor from Arduino IDE open as well? Or maybe Arduino IDE is still connected to your Arduino?
In case that is not the issue do you mind sharing a screenshot of the error message please?
@becburmeister: well yes, PLX DAQ is supposed to fill in data to Excel and not just display the data in the DirectDebugWindow. But for PLX DAQ to correctly understand the data, parse it and paste it to the sheet it has to be send from Arduino via Serial.print in the correct format. Please take a look at the BeginnersGuide Word document included in the v2.11 zip file for easy to understand details and examples.