just as a thought, this 400 limit could be a mental cap for you... i know when i built my first
bankroll from 20 to 1750, i had to overcome 2 mental caps, the first of which was at 100 $ where i would just hit a wall and not seem to get over the 100$ mark, the second wall was at the 1000 mark, where once again it took a very VERY long time to get over that mark and keep it over it...
i find that if you hit a point where you start thinking "i dont want to loose this" and change your play style than you will loose it because you are no longer playing optimal poker.
So, as my little addition to this conversation, there is a possibility that you need to just turn your brain off to the money aspect of the game (i know its hard to think about...)...
Phil Ivey said it best when he said something along the lines of "When you start thinking this is enough money for a car, or a house i could be loosing (or a beer for micro limits), than you are already lost" ..... Essentially you have to look at it as a game to win all the chips, the money will follow... if you concentrate to much on the money aspect and the "Oh man i lost X" than you are already going to loose...
Hopefully this little ramble can be of some help...
2 main points..
1) Try to play consistent poker, that mental block at certain levels will only hurt you
2) Dont think of it as money or "what i could loose", think of it more as a game, where you are trying to collect all of the chips, so you can make the correct calls etc... (Scared money, is lost money... hence the reason for Bank Roll Management)