Make sure your map path is identical to the "guy" that saved the replay.
For example, for playdota it's normally:
Warcraft III/Maps/Download/DotA 6.7xxx
But you can also find
Warcraft III/Maps
Warcraft III/Maps/DotA
etc.
So what I mean is this - Your map has to be in the same folder as it is of the guy that saved the replay.