yea they maybe spec type maps as in they have a terrain you don't have at all in your pff file. get a tool change them Bms to Mis you see it with the med file if the terrain is all black in color then you don't have the terrain at all.
map makers should add a text file to say what they have added to their data base as in exp2 to their game or custom terrain so other know if it going to work or not.
"Delta Force Skins/Mods :: Delta Force 2 Mods"
before you add them in make a folder and copy and past all the pff files in to it (put the folder inside DF2-game folder), reason if some thing don't work out to good you can change it back.
then instill the new mods (add in new terrains and other thing) you should be cover then and the map should work then.