I don't think this fault is for a seat occupancy sensor but more a seat position sensor similar to late renaults etc.This,as you may already be aware,lets the srs ecu know how close the seat is to the airbag/s to control how much the airbag inflates in an accident. These sensors,if like the renault ones, are easily dislodged off by rough use of vacuum cleaners under seats or debris in the seat runners.
Also, asyou may of tried already,try disconnecting underseat plugs and spraying electricalcleaner on them. HTH,Gary