Properly loading a file, and the ability to select the AudioStream seem to be issues for many users. It took me some sleuthing to find the answer to both problems, and I think a future version should fix this or at least add an explanation of the problem.

Here are the answers...

If your mkv video won't load, check **the entire file path** for odd characters (e.g., C:Documents and SettingsTom & JerryDesktop [or My Documents] won't work because of the "&"). Best bet is to move the mkv from wherever it is straight to C:

If the file loads but you can't select an AudioStream, it's likely because the embedded Audio file is Track 1 and the embedded Video file is Track 2. They need to be flipped. Here's the answer: http://www.trustfm.net/phpBB2/viewtopic.php?t=1856

I just fixed my mkv file, it in C: loaded it up selected the audio stream. Worked like a charm.
(I can only assume that a similar fix is necessary for an AVI that won't load or let you select the AudioStream, but I haven't tried it.) Took me a while to find this, and a lot of people have this issue. Please pass this along.

Jon