I've finally found a reference to the issue, apologies for double posting it.
If you're having a similar problem, please look here: http://www.adventuregamestudio.co.uk/forums/index.php?topic=42335.0
I've also worked out if you don't want to turn off the lip sync, then changing the letters which the animation will be played in the box next to it will also allow you to use more frames (but just on the letters you specify).
If you're having a similar problem, please look here: http://www.adventuregamestudio.co.uk/forums/index.php?topic=42335.0
I've also worked out if you don't want to turn off the lip sync, then changing the letters which the animation will be played in the box next to it will also allow you to use more frames (but just on the letters you specify).