Had same problem. Cut-out switch which is engaged when you fit the bag (hook sticks out at bottom of bag) is not being engaged, (over-ridden, activated) and thus engine cuts out when you engage blades cos m/c thinks you have no bag.
My solution: I put a small piece of stiff carboard in the hole so the hook penetrates further and pushes in the switch. Works fine for years apart frpm the occasional need to reseat or replace the cardboard!
Barrie Lipscombe
September 2011