Conversation so far:
what was proposed about the European Flag?
The barcode seeks to unite the flags of the EU member countries into a single, colourful symbol.
what kind of symbol?
CANNOTANSWER.
why did they decide to unite the flags?
Koolhaas and his think-tank AMO - an independent part of OMA - suggested the development of a visual language.
was there any opposition to doing this?
The logo was used for the EU information campaign, but was very negatively criticized.
was the proposal successful?
The logo was used for the EU information campaign.

Question: when did all this happen?
Self-contained rewrite: when did  EU information campaign happen?