Vauxhall Vectra indicator lamp continously on when headlights or parking lights are switched on

I have an alarm on the dashboard indicating i have a problem with the lights. The indicator light on the front left hand side, is continously on when either the headlights or the parking lights are swiched on, this apparently has stopped the parking light on that side from working. When you swith on the indicator or the hazard light the light flashes as normal. Any assistance to deal with this will be greatly appreciated. Thank you!