I am reviewing the product information for your AV receiver from here
It appears there are at least four models of ipod docks for your model receiver: ASD-11R, ASD-1R, ASD-3W, and ASD-3N.
The users manual for your receiver does say that in its default settings, the VCR inputs are used as ipod inputs, so it sounds like you are certainly following the manual correctly for defaults. You can custom-assign the iPod to a connector other than VCR (using the GUI menu “Source Select” – “(input source to which iPod dock assigned)” – “Assign” – “iPod dock” (page 42). It might be worth following this up incase for some reason your default doesn't happen to be VCR - it may be looking (listening) somewhere else.
If you have the RF Remote Controller (RC-7000CI) or RF Remote
Receiver (RC-7001RCI), these devices are supposed to allow you to browse your ipod when connected, and would therefore be helpful in ascertaining that the denon was recognizing the ipod but not playing the music, or not recognizing that the ipod was connected period.
I would certainly review the Play, Playback, and Assign menus regarding your ipod dock configuration, as well as make sure my ipod had the latest firmware updated. (I have seen the latter be the deciding factor.) There is also a firmware update for your receiver at the link I posted at the top, and it never hurts to keep components up-to-date, especially when they aren't behaving the way the ought to.
I hope that helps.