Stopped mid movie and said not valid format

I had the old WD TC lice and got the new on recently however it has stopped playing mid movie twixe now saying that the file I was playing was not a supported format however I am playing and MKV which is supported. Played fine for the first 20 minutes and then I had to power cycle it to get it to play the rest of the movie. Never had this problem with the old unit. Anyone have a similar issue?

Also everytime I start my device it tells me that the last conent source was removed. Any fix for that?

Try playing the same file from another USB memory or external hard drive. Also check if you have the latest firmware version installed. 

Try a different movies to make sure it’s not a bad file (rip).