After an investigation, it emerged that TBWA's campaign for Amnesty France did not appear in the media between 1 March 2007 and 30 April 2008, as required.
The festival chairman, Terry Savage, said: "While it is not our policy to discuss specific cases, if we have doubts about a specific entry, for whatever reason, we will fully investigate the matter to its conclusion."
He added: "It is important for the advertising and the awards industry that entries made fully comply with the rules and spirit of the festival."