I want to access COM alternately from two programs

[314w]

I am writing a control program in C#
I want to start two programs and alternately access COM3 (USB address: ASRL3::INSTR).
However, in reality, you cannot operate it without closing one of the programs.

But I was able to do this before.
For instruments with USB address USB0::0xaaaa::0xaaaa::aaaaaaaaaa::INSTR.

At the beginning of the program we declare "using NationalInstruments.Visa;".
It cannot be resolved by "Dispose" of "MessageBasedSession" after communication.

What is the difference when recognized by COM?
Also, is there any way to solve this?

.........Google Translate.

[santo_13 · Accepted solution]

Better create another appC which will be the gateway for the COM port and appA and appB will communicate with appC for any transaction with COM port.