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Another community member (Rstr) experienced the same error in the second page of this discussion: Missing file : Wifi.msi when installing driver update
The correct answer and other suggestions are given in the first page.
Thanks Joe, I saw this thread but as the description of the error was different I didn't think it would resolve my problem.
I found the files Wifi.msi and Wifi.cab files in the temp directory and copied them to the C:/Windows/Installer folder as suggested.
This solution fixed the error and the upgrade completed without a hitch.