54In that context, when, in the dialogue provided for in Article 84a(3) of Regulation No 1408/71, the institution of the Member State to which the workers have been posted puts before the institution that issued the E 101 certificates concrete evidence that suggests that those certificates were obtained fraudulently, it is the duty of the latter institution, by virtue of the principle of sincere cooperation, to review, in the light of that evidence, the grounds for the issue of those certificates and, where appropriate, to withdraw them, as is clear from the case-law referred to in paragraph 43 of the present judgment.
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