Boris mocha roto problem

OleSouWester Posts: 3 Just Starting Out

Hi, I am having some problems when using roto with mocha. When I start tracking, I get about halfway (short 8 sec clip) and then it freezes, and I get the following error message: 'One or more layers not tracked properly. Try increasing the minimum percentage of pixels used'. This is all well and good, but how do I change the % of pixels? I can find nothing in Boris or Hit film manuals that mentions this, apart from one reference that says increasing pixels leads to slower renders but higher quality. Nothing on how or where to alter the settings though. . A simple explanation would and solution would  be appreciated.

Thanks in advance

PS no matter where I start tracking on the timeline, forwards or backwards, it is always the same no. of frames before it crashes