[boost] some mpl programming task -- don't get this compiled

I'm still unclear about some fundamentals of the mpl library. Could somebody have a look at this source code? I'm playing around with this since quite a while. I'm trying to convert some information into an array of strings. I'm using boost::mpl::map instead of vector as I want to overwrite points in a two dimensional matrix. So in fact this is a map indexed by a long containing another map indexed by a long containing char. Two dimensional quadratic matrix of char. Thanks Peter