Advancing the c6 pawn in the Caro-Kann I am having trouble understanding when Black should move c5 in The Advanced Variation of the Caro-Kann. 
I have posted two games of mine below:


In this first game, after the seventh move of White, the computer has no quarrel with the pawn advance c5 (though I played Ne7).
However, here:


Which is a really similar position, if I play c5 (on the 8th move),Stockfish tells me it is not the right thing to do, but rather I should have played Ne7 which is a move also acceptable in the former position.

My question is: does anyone know when is the advance c5 appropiate? I cannot see any reason why these positions should be differently evaluated at all.

I mean in the second position I find no particular reason why playing c5 which in case of being captured allows the direct development of my kingside bishop can be a bad thing at all.
The knight on c3 is the difference.  In the second position, White can exploit superior development by quickly opening the centre with c4.  It's not easy for Black to arrange castling.