Why mono sound?

[tcb1967]

I use MF3 and LG RC7100 standalone player.
I've recorded several TV-series using my standalone player (using DVD-Video mode) and have finalized the discs. When I watch the series with my LG there are no problems.
Problems start if I would like to edit some series using MF3. I import the material alright, but the sound is mono! I've tried everything I could imagine - what could be the problem and how to solve it?