serial communication

Question

I have written a program in VB.NET 2008 to transfer n receive characters from one PC to another through serial communication(RS232).

I am getting an error as

"AN UNHANDLED EXCEPTION OF TYPE SYSTEM.INVALIDOPERATIONEXCEPTION OCCURED IN SYSTEM.DLL
ADDITIONAL INFORMATION: THE BASESTREAM IS ONLY AVAILABLE WHEN THE PORT IS OPEN "


But i get this error .So plz reply ur valuable answer.

my id is [email protected]

Thanking U in advance..

Regards
Indu