The ASA received complaints from three members of the public about the ad which showed a man sitting on a sofa with a beer, beside a woman standing in a figure-hugging dress with the label still attached, and the text: "Take Courage, my friend."
The ad reprised a famous ad slogan used for the Courage brand for 30 years until the 1980s.
The ASA ruled that despite the humorous intention behind the ad, it contravened the advertising code of practice by suggesting that "the combination of the text and the image was likely to be understood by consumers to carry the clear implication that the beer would give the man enough confidence to tell the woman that the dress was unflattering".
But Wells & Young's marketing director Chris Lewis said he was surprised by the decision.
He added: "We have both pre-cleared this advertising with relevant industry bodies and worked closely with the ASA to resolve this issue so are naturally disappointed by the outcome.
has been used in Courage advertising for decades and this recent poster campaign brings this iconic beer up to date in a light-hearted manner."