Serial comport communication using wcf services

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C#5.0

WCFServices

Writing method in wcf seervice for write data on comport:- COM1

if (!(comPort.IsOpen == true)) comPort.Open();
                       //convert the message to byte array
                       byte[] newMsg = StingToAscii(msg);
                       //send the message to the port
                       comPort.Write(newMsg, 0, newMsg.Length);

when i call method then first time write data on port but second time get error:-Access to the port 'COM1' is denied.

when I comment this line

//if (!(comPort.IsOpen == true)) comPort.Open();

then get error :- Comport is Closed

please Suggest me. Its very ugent.

Thanks In Advance

Chandrashekhar