BTW Popej, if you use the standard Windows zip function, the archives are compatible with Apple's archive utility that's included with every Mac. I don't know why, but archive utility couldn't decode your 7-zip file so I had to download the suggested keka program.
I use the standard windows zip files for the maps I make because that way I know they will open on a Mac without any special software. Come to think of it.... I wonder how the OP decompressed the archive? That might be the problem.