How to resolve 'com.apple.buildinfo.preflight.error error 21' when reinstalling Monterey on iMac?

I am getting this message when trying to reinstall Monterey and despite using Apple first aid and Disk Warrior I still cannot start my iMac

[Re-Titled by Moderator]

iMac 27″, macOS 12.7

Posted on May 5, 2025 06:40 AM

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1 reply

WheelieNick

Level 8

45,461 points

May 11, 2025 02:38 AM in response to grumpyman1

Have you tried installing Monterey on an external drive to see if the issue are caused by your harddisk? If yes, it might be an issue within the software target disk In the installer. if that is the case, you may need to Contact - Official Apple Support so that apple can look into it

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How to resolve 'com.apple.buildinfo.preflight.error error 21' when reinstalling Monterey on iMac?

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