Gerard,

First I'd use http://support.microsoft.com/kb/311272 and run the utility as:

devcon.EXE RESOURCES =ports >c:\ports.txt

and post your results here.

Next, download Portmon.exe from http://www.microsoft.com/technet/sysinternals/utilities/portmon.mspx and set it to capture all serial ports. It should log any port activity and give you the application's name that is using those ports.

>Hi.
>I am trying to output to a serial port , but I get an error message. Uisnf a serial Port analyser, it says the serial Port has lkaready been open by another app, but I cannot identify which app, and there is'nt anything obvious running which uses the serial port.
>
>Anybody know of a way of identidying which process has the serial port open, or is there a way of closing the serial port from a different app ?
>
>Regards,
>Gerard