This is a totally geeky issue, but since this problem took me all afternoon to fix and then another 90 minutes on a paid tech support call with Apple . . .
I hope to save you that same agony with this short video.
There is a safari problem downloading zip files.
The slightly embarrassing thing – for both me and Apple, is that the solution was so simple and took us so long to figure out;)
As I experience tech problems (which is often due to not being very smart . . .) I will make videos of the solutions and put them under the “Tech Fixes” category.
So, if you have a MAC and ever have problems, check here before spending any money on fixes!