the operation couldn't be completed because the file is still being downloaded error

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I'm trying to download some large rar files (20gig) and when I check progress I get the above message and the download has stopped. Ive tried the download on my iMac and my MacBook and the same thing has happened in both cases. Ive never come across this before, can anyone help?

For the record its pictures and bits and bobs for Football Manager 2020 from the sortitoutsi website.