xenon light problem

Hi

I'm really hoping one of you clever guys can help me... I changed the xenon bulb in my e60 BMW and now when I switch on the headlights all the lights go out... Side lights and angel lights work fine but all goes off when I switch on the headlights... What could cause this? Any advice here would be much appreciated!!

Was the replacement bulb exactly the same kind and power as the original bulb? A HID bulb is completely different to an incandescent bulb.
Or was it a Cheap (you know from which country) fake bulb from ebay?

What is the battery voltage when the main headlights are switched on?
Does the BMW have a separate battery for the lights?
Maybe its a dodgy bulb and its actually oscillating on/off at such high frequency that it looks on all the time....the high frequency is creating noise which kills the driver circuit for the side lights etc?