I am getting this error message : this map has too many colours; and must be dithered to 112 colurs.

The problem is the map I am trying to load has only 12 Colors!!! (according to gimp's color anaylsis.) so why am i getting this error message? thanks

Maybe 12 colors are too less. Try using at least 64.

Did you save it as a 256-colour PNG?

If so, look at the file's palette PNG chunk with TweakPNG, as there may be unused colour entries in the palette.