You're not the only one with this problem.
I'am living in The Netherlands and own an 'official' dutch Denon AVR-3808A.
I've got a brand new computer with Windows 7 and the latest release TwonkyManager.
After a while, not always at the same time or played track, the stream stops and the current track will be repeated for ever.
Only a power-cycle with the litle power-button solves it, no changes or restart needed of the computer running Twonky(Manager).
I know, this solves nothing but now you know that you're not the only one
At the time I wrote the text above Denon released a new firmware-update.
I updated to the latest firmware which took only 15 minutes (from previous firmware, update from older firmware versions wil take longer)
After 2 weeks I can say the problem with hang-ups while playing network audio is solved.
I even saw no more messages 'Server Disconnected' after a day or 2 not listening to network audio.