Well that sucks, please let us know if you make progress.
Been working with PlayOn support staff and it looks like an issue with WHS2011 more than it is with PlayOn. Here's the details:
Server - WHS 2011 booting off of SSD with FlexRAID for storage. No AV and just the stock Windows Firewall.
#1 - Security restrictions on WHS 2011 will not allow you to test your login with NetFlix or Amazon Prime. Works fine for Vudu and HBOGo.
#2 - PlayOn will not stream to HTPCs in HD unless you are running Kodi v14 or higher.
#3 - PlayOn requires an audio device on the server
PlayOn support had me trying a couple of things to try to work around it but not having any luck. The biggest problem is that WHS 2011 will not recognize any audio device. Most attempts at driver installation stall with an error message that WHS 2011 won't support the driver installation. If I find a driver that will install it literally just ignores the installation.
Trying to access NetFlix and Amazon completely fails on the HTPCs.
If I run the PlayOn server in 'User Mode' (Press CTRL when you click <Start Server>, then I am able to select the media files and PlayOn attempts to play them back but then just pops up with the error message that "PlayOn Server could not detect an audio device. Please reinstall PlayOn." So I did with no difference.
To test things out, I installed PlayOn on my desktop tower with Win7 Pro. I am still running XBMC v13.2 on my HTPCs so everything was limited to SD (a lousy SD at that). I installed Kodi v14.0 on my laptop and ran it from there and it was smooth and easy. Even though it is limited to 720p, the video quality was actually better than I expected when you consider that PlayOn transcodes everything to MPEG-2 before streaming.
Anyway, I had been thinking of moving from WHS 2011 to Win 7 Pro or Win 8.1 Pro anyway so it looks like I may end up doing that sooner rather than later unless I can find a way to get an audio device installed to my server in the next few days.
I'm actually quite impressed with PlayOn and kind of wish I had tried it sooner. One huge complaint is the thumbnail resolution is awful, probably 180x120 or something similar. I am used to 600x400 or better.
----Incidentally, looks like there was an update to PlayOn last night. There had been talking of supporting MPEG-4 transcoding for Kodi instead of MPEG-2. Looking forward to installing and finding out----