There are lots of HEX editing programs out on the internet, like HEX Workshop, HxD or Cygnus. If its this over your head I think it would be best to just PM me an .ips file of your hack so I can see what's happenning and hopefully get it straightened out :P
It seems like you've set your border on that map to be the first tile in the regular FR tileset. While it may look black in A-Map due to the palette that it is using, the tile is actually completely transparent. Just change the border to some other configuration of tiles and it should look okay.