Hello Wolfgang,
To add to Mark's reply, in case it's relevant, in Hauptwerk v8.0.1 or v8.0.0 if you're routing directly to a primary bus (not via a group) then please make sure that your primary bus is also in at least one group (e.g. use a group such as 1024 as 'dummy' group to put it in -- no need actually to route any ranks to the group):
viewtopic.php?f=4&t=21023&p=157122#p157122If that isn't the problem, and if the problem occurs again, then please try looking at the green/red virtual signal activity LEDs on the three audio routing screens as Mark mentioned, and also look in your audio interface driver's control panel to see whether it's showing signal on the relevant channels.
Best regards, Martin.
Hauptwerk software designer/developer, Milan Digital Audio.