This Developer tool should be automatically and manually tested before a new release! Not after the fact. Don't treat web developers as a second class citizen.
Also, the advice isn't workable. There's no apparent place for Preview 125.
Preview 126 can't be used, because it requires OS X 12 beta.
A web developer should not upgrade their work machine to some beta operating system just because Apple QA is lacking.
monfera
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I fixed this error message by a simple execution of XCode> Product> Clean Build Folder
I don't know how or why the error even incurred, or what the nature of the problem is, though I upgraded from a beta to an RC so stuff like this isn't unexpected