Unable to open serial port in .NET

Question

I am trying to open COM1, but get a strange error every time I call SerialPort.Open().

The error is:

The given port name does not start with COM/com or does not resolve to a valid serial port. Parameter name: portName

The code is very simple:

SerialPort port = new SerialPort("COM1", 19200, Parity.None, 8, StopBits.One);
port.Handshake = Handshake.RequestToSend;
port.Open();

If I call SerialPort.GetPortNames(), it returns one port called "COM1".

I've verified that I have a "COM1" on my computer, and I'm not using it in any other applications. When I run the code on another computer, it works. My system is running Windows Vista. The version of .NET is 2.0.

Is there a security setting I have to change somewhere? I'm logged in as an admin, and have UAC turned off.

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More info

I used Process Explorer and confirmed that nothing is using \Device\Serial0.

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Workaround

I installed a USB-Serial adaptor (COM3), and it works fine. Go figure. There must be a problem with COM1.

Answer 1

I had this problem too. It turned out that I had a printer set to use the COM port I was trying to open. Once I changed the printer to use another port the port opened just fine.

Answer 2

Try to use the notation \.\COMX instead of just COMX. Ensure you escape the characters: "\\.\COM1"

Edit:Wops, SO escapes my \ so it should be like this (ommit spaces): "\ \ \ \ . \ \ COM1"