Issue with new firmware version 2.03.20. No longer plays MKV files

try a Factory Reset 1st …

Setup > System > Device Reset > Reset All Settings Back to Factory Default

if that doesn’t work … my Firmware Rollback Guide is HERE

Note: there is no download link for Firmware 2.02.32 on WD’s Webpage

So if you need that version … here’s the download link (but you will need to edit the *.ver file to a higher number for the WDTV to detect it eg.VERSION=‘2.02.32’ to VERSION=‘4.02.32’
http://support.wdc.com/KnowledgeBase/answer.aspx?ID=5860