ICMs are professional events, attended by thousands of mathematicians. There are Planary talks and Invited talks with first rate contributions by specialists. All of them are recorded in the proceedings volumes.
And then there are Contributed talks, and Posters, which are not recorded in the proceedings, apparently. And this seems to be leaving the door open to virtually any claim. Indeed, one can find there a mix between regular graduate student or postdoc contributions, and, shall we say, more dubious material.
In fact, in 1998 in Berlin, nothing suspect pops up among the talks announced in time, but the google cache tells us that the accepted late submissions included “Fermat’s Last Theorem, a Simple Proof based on Irrational Numbers“, and “NP = P“.
Unfortunately, I couldn’t manage to find the ones from 2002 in Beijing.
But, nil desperandum, there were also noticeable revelations in 2006 in Madrid, including “On Fermat’s historic marginal note: some significant left-out grains of truth leading to new proof of FLT“.
In 2010 in Hyderabhad, lots of creativity was again to be found, including “Four Errors in Cantor’s Proofs on the Uncountability of Real Number Set and The Foundation of Mathematics“, but also three new proofs of FLT ( “Fermat’s Last Theorem“, “Proof of Fermat’s Last Theorem (FLT)” and “Proof of Fermat’s Last Theorem“).
The 2014 one in Seoul promises yet more of the same, including “How to prove the Riemann hypothesis” (based on v16 of this paper, apparently).
I don’t quite understand why all this is allowed to happen…