playing .mkv files

the down loaded big buck bunny divx7 .mkv plays fine on my blu-ray but when i use divx7 divx plus to create a .mkv file it wont play on my blue-ray all will play fine on computer have registared my blue -ray any ideas pls

What kind of Blu-Ray Player

What kind of Blu-ray player do you have? Blu-ray players that support DivX Plus HD, which is H.264 video, AAC audio, and .mkv container, will have the "DivX Plus HD" logo. If your player has "DivX HD" or "DivX" on it, it probably is not DivX Plus HD certified, and therefore, cannot play MKV, unless the manufacturer tried their own implementation (in that case, you'll have to contact them for support).

If you tell us the player, we might be able to find out more...