Loading and Unloading Issue

Our insured received a delivery and sent two employees out to unload the vehicle; this vehicle is not owned by or rented to our insured. The employees rested a ladder (this is owned by the insured) against the delivery truck. While they were unloading the truck, the ladder fell to the side and struck a parked car owned by a customer of the insured. The resulting property damage claim was reported to our insured's business auto insurer which denied coverage.

Would this claim be covered by the CGL form?