Volvo Repair: 2001 V70XC rear brake lights, brake light switch, light bulbs

Question
I have this V70XC since new. Three weeks ago I noticed the 'check rear brake lights" warning came on. I checked the lights and found the two side brake lights went out. I check all the fuses and light bulbs and replaced the suspicious ones. But the lights are still not working. I even tried to check the relays but I can not positively identify which one is related. In stead I moved relays around to see the symptom may change nothing.  Can you give me some pointer what else could be wrong?

Answer
Pull all the bulbs out and check to make sure the sockets are making a good connection.  Sometimes they;ll get in position, but won;t light up because of that.  Also check that the bulbs are EXACTLY the same from left to right sides.  If they are different, the bulbs may work but you could still get that message.  There are no relays that control those lights, just the brake light switch.  If the message is coming up you are getting power through the fuse and switch so you need to check the wiring near the bulbs if nothing else is found to be wrong.  

James