nakchak,
thanks for your suggestion. I do not need the external reset, so I have not implemented that.
But I just made some significant progress:
The problem seems to be related to the software, at least in some way.
It seems that there is some interference with the Serial Port, defined as:
[font="'courier new', courier, monospace;"]ReadPort = new SerialPort(SerialPorts.COM1, 9600, Parity.None, 8, StopBits.One);[/font]
If I don't use that port, then the software reset seems to work.