Problem opening serial port

I am developing a windows mobile application but have recently came across the error message, Unable to open serial port 'Com4' LastError=AccessDenied.
It was working okay one minute and the nhext time i tried to change the port this error came up, does anyone know how to get rid of it???

Thanks in advance John.

How do you mean - 'I tried to change the port'?

Did you close the port before re-opening?

Pete

I'm simluating sending text messages using the Cellular Emulator but when i try to change Serial Port 0 to COM4 as it is on the emulator it displays the error message.

There are some 'How Do I' videos on the cellular emulator here