Yes, at least once, for the Rosetta launch. The damage was discovered before the launch:
A fallen chunk of foam insulation from the rocket’s fuel tank scuppered the latest launch attempt. During a final inspection of the Ariane-5 launch rocket at 0100 GMT on Friday, a 10 by 15 centimetre chunk of foam was found on the movable launch “table” that supports the rocket.
The 30-metre-high cylindrical main stage of the rocket is covered with foam to keep its cryogenically cooled liquid oxygen and hydrogen fuel from heating to the tropical temperatures of the launch site in Kourou, French Guiana.
If the launch had proceeded, rocket operators say water vapour in the air could have cooled to form a 100-gram block of ice on the exposed surface. During flight, the ice could “separate and cause bad damage”, says Jean-Yves Le Gall, chief executive officer of Arianespace, the rocket’s manufacturer.