I don't know how to help/support you. A sample would be my whole project - a bigger one. I try it now with a smaller tool and hope to get the same error but I don't use there a network connection - only debugging via USB. The sourcecode of the main program is the same as on NetDCU6 and I had there no problems.
Interrupt happens irregular and occasionally - I can't reproduce it. Today I needed about 60min to get a lost connection. It is generally very short - after one second connection is there again (browse with ActiveSync works again), but Debugger was closed and program hangs (when debugging). In release version the program does not hang, but network connection is lost.
Also the network connection works again quickly after interrupt. Unfortunately I have to close the socket of my program and open it again manually to continue communication. An automatic recognition of interrupted network connection is not possible.
It seems that both (USB and network) are interrupted together.