Error Validating Fonts in Font Book

Are you trying to install a massive amount of fonts? Typically Font Validation is that the Mac is extremely hyper-picky about the integrity of the fonts it installs. Most fonts with minor validation problems should still be installable (and work fine for 99% of whatever you need them for) and only fonts with significant standards-conformity problems will be completely blocked from installing.

And NVRAM reset would have no bearing on the font install process (moreso than just doing a plain restart).

If you're specifically saying that the same individual font can't install, but then you restart and do a first aid and that exact same font CAN install I would go into Safe Boot Mode (shift on startup) which will clear out the font caches and (for good measure) run another disk scan there.

And if this still happens, are again... you're talking fonts that won't install, then will install, this does point more to a disk utility or system problem.

And just to clarify, are you in the process of installing a huge quantity of fonts or something?

Hello Yavno,

Thanks for reaching out to Apple Support Communities.

We understand you are experiencing some issues with using Font Book and installing fonts on your Mac. We are happy to help provide some guidance on this with you.

We have a great resource that goes over how to install and validate fonts in Font Book. We want to make sure the steps listed are the steps you are taking to install fonts:

Install and validate fonts in Font Book on Mac

If those are the steps being followed and are getting error messages, let's try rebooting the Mac in Safe Mode and trying again to see if the same issue persists:

How to use safe mode on your Mac

Let us know if you have any questions or if the issue continues.

Best Regards.