Roy,
I'm assuming you're using internet explorer.
try this-
go to tools>Internet Options. Click on 'privacy' tab. Then click on "advanced."
Check the box that says "override automatic cookie handling."
Then, check "prompt" in both boxes for first and third party cookies. Uncheck the box that says "always allow session cookies."
Then hit OK, go back to the "general" tab and hit delete cookies...when it asks you to delete all files in Temp. folder, hit OK.
Hit OK again to close that box.
Then you'll be prompted to either accept or deny each cookie offered. You can narrow it down that way. It's a pain, but you'll eventually find the nasty one...it's probably something from "ads.quickserve.net" or something similar.
Process of elimination.....good luck
Mike
NB- when you delete cookies, you'll have to re-logon to the CB, etc...