My 05 525i has had a rear brake light error on constantly for two weeeks now. The lights are operating fine. I have changed the bulbs on both sides and still receive an error. I note the battery is on the way out as its nearly four years old. I keep having to set the time/date and the "excessive batery discharge" error comes up if I use the radio for about 5 minutes without car running.

Any ideas???? :(

It sounds like making a trip to the dealer is in order.

is your 3rd (middle) brake light ok?

if you are getting a brake light warning then its your outer most bulb that is at fault here. You say its working fine. But have you removed the bulb from the holder and checked the holder itself. It could be the bulb has not seated itself well or there is some corrosion etc in the holder.

let's get a new battery first.

what?

+1 on the Bulb sockets and check for a clean surface on the bulb contact. The slightest of corrosion will cause a bad read on start up.

Bruce,
You were spot on. I wasn't looking hard enough at the bulbs and yes it was the outer most bulb. It was burnt looking but still illuminating.
Thanks again.
Jarrod