Trouble updating Add-on

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I'm trying to update to a calendar from 1.2.1 to 1.4.4. However when I try to download and install the latest version via my dashboard, I get:

"The following errors occurred when attempting to process your request:

There was an error unpacking your add-on or theme. Perhaps you have not uploaded a valid zip file, or you do not have zip installed."

What am I missing? Do I need to install a zip Add-on?