No Random Access on Movie

[martinthehugh]

I tried playing a HD movie (Skyfall) stored on a Freecom external USB drive, plugged into the Raspberry Pi running Xbian.

It plays fine, but I cannot move to a different position in the movie by clicking the position bar which runs along the bottom edge of the movie. I can do this on other movies which may be lower resolution DiVXs (this was a .mkv)

Is there any known limitation of hardware, software or file format which would prevent me changing the position in the movie.

As background, I watched this movie for an hour and a half before Xbian crashed out back to the main bubbles screen. The file is fine, and plays in other media software. However, once I had restarted the movie I wanted to jump to where I had got to, but Xbian insisted I had to watch it from the start or not at all.

Your thoughts please.
Thanks