There is a firmware update at Denon's site for the 2910 with "HDMI" improvements listed as being one of the items fixed..

Go to the 2910 page and select manuals and downloads, you will find it there, it will ask for the serial number of the player and should be able to tell you if it needs an update.

[Link: usa.denon.com]

Check HDMI Notes on page 16 of the manual,
Also check in the set up that the:
-HDMI/DVI select is set to HDMI (Factory setting is off)
-Output format selected for HDMI matches the format that the display is capable of
-Video output setting for "Pure Direct" is not set to Video:Off or All:Off