Groove Agent installing issue - archive is not readable

Hello forum people,
I bought the Absolute 3 pack about a month ago, and have not managed to successfully install Groove Agent 4. Using the Steinberg Download assistant, I have downloaded and saved the file When I try to open I get a message “Archive is not readable. Would you like to try a password?” I have hit a dead end here.

I tried downloading the zip file separately from Steinberg’s site (i.e outside of the Download assistant) but still have the same issue.
To prove to myself I wasn’t being totally stupid, I did manage to successfully install the “Dark Planet” vst using the Download assistant. I’m not doing anything differently but the Groove Agent file is just not opening. I am getting quite frustrated now as I raised a support ticket with Steinberg, and 15 days later it remains unacknowledged, which is quite poor.

Would be so grateful if anyone here know how to solve this?