Are you sure... i.e have you changed it and it is Ok now???
I had exactly the same problem last year and it turned out to be something even simpler and a recurrign S1 fault.... underated starter relay fuse. Mine went intermmittent and was really hard to spot as blown or not. If your starter fuse is 20A then change it for a 30A and save yourself quite a few pounds.
BHM seem sure - they swapped it out and put the magnet back into the right place and she started every time - and she's had a 30amp starter relay fuse upgrade already. All fuses were fine when it broke down - so I knew it was something else...
Bugger of a job to change this switch, apparently...
I think this really is a case of too many electronics; why a magnetic induction microcircuit when you could either:
a) use a microswitch, or
b) not bother with a switch at all, trusting people to not start their cars in gear.
I guess it would have been too much hassle to re-engineer the X5 electronics, designed to stop school run mums from accidentally running over their offspring when starting up their battle tanks...
