Can WD TV series play .ISO files?

I think the difference between the ISOs that work for you and the ones that give an “unsupported format” error could easily be due to the size difference. For whatever reason, the WD TV Gen1 doesn’t play ISOs that are less than about 30 minutes which is a common length for TV episodes. While not very well documented, you can find information on it if you poke around other forums. Maybe if we bring it up enough, it’ll get fixed. The workaround seems to be to use an MKV container instead of an ISO container.

http://wdtvhd.com/index.php?showtopic=4334

http://wdtv.uservoice.com/pages/17442-general/suggestions/182950-dvd-iso-support-for-chapters-shorter-than-30-mins?ref=title