James I have two TNC 4 units.? I got both working once and now that I am trying to get them asigned I'm running into the same issue.? Windows sees them and connects but then quickly disconnects.? It never assigns a COM port but it does remember the device.? I know this is a driver issue that I fixed once but cannot remember what I di.? Once the COM port is assigned YAAC talks fine to these units as a KISS TNC.? I used it for a few hours locally.? Can you help here or maybe on email?? Sharring the final solution here would be a great help to many people.