WDTV locks up when playing high quality mkv file

I use makemkv to rip my blu ray collection and recently I have noticed that some films with HD sound can’t be played by WDTV.
This is It plays the video but the audio keeps on cutting out and The Surrogates gets about 5 seconds into the film, the screen flashes black with a green line and the unit locks up. The white lights remain on but I had to power the unit down to get back to the menu screen. It is almost as if the unit is not powerful enough to play the films? It is really annoying and makes me want to buy another player but I don’t see why I should have to when this one should work and I liked the thumbnail view that the WDTV offers.
Please help! (Using latest firmware)

My WDTV doesn’t lock up but it stopped playing the audio on mkv and other hd video file formats a couple of weeks ago after giving me a year of trouble free service.  I think I’m using the latest firmware - 1.03.01 and wonder if going back to an earlier version would resolve the problem.  Any thoughts?  Can anyone point me in the direction of where I can source earlier versions of the firmware?  I would even try ‘unofficial’ updates - any out there?  Thanks.

I’ll bet you downloaded a video made with MKVMerge 4.1 or later.   

That’s a known issue.   If you search the forum, you’ll find PLENTY of answers on how to fix it.

The mystery for me is why did all my mkv and other 720p files all play perfectly well, with full multi-channel sound, until a couple of weeks ago, then all of a sudden no sound at all???