It happens with any zip file or just that zip file?,
Maybe you tried to download the zip file and the download was interrumpted, and the zip file got corrupt, so you could try to dowload it again.
It still unable to open it also could be that the zip file as is on mediafire is corrupt, probably when was uploaded got interrumpted.
Check you are trying to open the zip file with the right application, could be directly with windows internal file handler or with winzip, winrar, z-zip, etc.
If the problem persist, You could ask to a friend to upload the map you want in another site diferent than mediafire.