Problem with Decompression in Mac version

I'm downloading the full demo (977 MB) via the 'direct' download for Mac, but when it finishes, in the downloads section of Safari it says that the 'Decompression' has failed and I can't unzip the file. The two downloads I've made of the file stop at different times, both around the 750 MB mark. Can anyone explain why this is? It is definitely not a problem with my internet stopping or slowing down or not working.

I'm also trying to download the Mac torrent, but this will take ages, so any help with the direct download would be great.