First of all they say that the document, even with a disclaimer that says that it may not be supported by the OECD or any of its state members, has the Organisation's seal and should be backed up or dismissed by them. The report, which cannot be found on the OECD's site but can be found at the websites of "antiethanol third parties" (their words), expressed serious concerns about ethanol made from grains.
The two associations state that in previous documents, the OECD has given full support to biofuels as a means of reducing CO2 emissions but the document is written from a partisan position that such an organisation should not be liable for.
They end the letter by countering some of the affirmations of that report by saying, for instance, that biofuels don't interfere with food supply or grain prices, that cellullosic ethanol is a reality or that biofuels are a reasonable solution to rising oil prices.
[Source: Abengoa via Energías Renovables]