Employee Lawsuit Covered by CGL Form or WC Policy?

Q

An employee of our insured was injured on the job and received workers compensation benefits. Then, the employee quit and sued our insured, the manufacturer of the equipment that caused the injury, and the insured's son who was a co-employee of the former employee at the time of the accident (our state allows co-employee lawsuits). The CGL carrier has indicated that it does not believe any coverage or legal defense is due because of the workers compensation and employers liability exclusions. We think that the insured is owed a defense but we are not sure about his son. What do you think?