Kramnik had seen that Fritz gets a new queen if he took the bishop on a6, and he saw no way to play on against the current material advantage of the program.
Mig Greengard analysing (after dipping into Kramnik's food supplies)
While looking at the game with Fritz and trying to find a plausible explanation for Kramnik's resignation, Mig was simply unable to trace out a clear win. So he started analysing the lines systematically and at great depth. The result: there is a very great likelihood that in the above position White can hold the draw.
Analysis during dinner: Frans Morsch, Tigran Nalbandian (Kramnik's second), Alexander Kure, Mig Greengard and Mathias Feist trying to find a loop-hole in Mig's analysis.
Mig's conclusions in a nutshell: Black will have a queen, knight, and passed b-pawn versus two rooks. But the black king is without shelter and the white rooks run amok. It is a very real possibility that Kramnik resigned in a position he could have drawn.
Vladimir Kramnik was told about the probably draw immediately after the end of game seven. In the press conference when asked for a reaction he said that he had obviously not been able to check the analysis yet but would do so, very thoroughly, but only after the match was over. "Until then I will put the whole thing out of my mind."
With this Kramnik follows in the footsteps of the man he succeeded in the throne, Garry Kasparov. In the second game of his rematch against Deep Blue in 1997, Kasparov resigned in a hopeless position only to later be told that with best play he could have drawn the game. You will find the full story here. It will certainly be a shock to Kramnik if that turns out to be the case here as well.
If you can refute these defensive concepts and find a forced win for Black please send this to email@example.com.