hi, i used to suffer from this , but it is one off two things ,
1;
your knee bar is not in the centre , so moving your knee inwards causing the pressure on your instep.
2;
your spring is not lined up , causeing your footplate to be un level . can be checked by using the jason string method ( not sure were the thread is ) them you can level by use of stabliser bars.
hope this helps
chris