HiTom,all,
This is from our webmaster on a simular thread:

>>The early C-track switch solenoids were not absolutely perfect when used in digital. The trouble was that they were "too good" and the tongue bounced back since the solenoid got too much "juice"... A solution was worked out by a member on the MML, and it consisted of hanging a 5 ohm resistance in series with the "yellow" wire. Märklin then also started to supply an extra resistor with the C-track solenoids. I however believe the problem is solved nowadays at the factory.<<

I would check the C-track switch mechanism it self and make sure it has no obstruction in it's movement.

Kevin!