Nexus 9 July OTA - now getting 'Device is Corrupt" error

I don't know if anyone else has gotten a July security patch OTA or not yet.

My Nexus 9 did this afternoon. Plugged it in, told it to install.
Do some other work, come back to it to the picture of sad little android on his back and 'no command'. No worries. REcovery is easy to deal with.

No worries, I'll just bring up the menu and reboot.
It does, and comes up with 'Your device is corrupted and cannot be trusted'.

Other than factory resetting it - any ideas on how to recover?
I will...

Nexus 9 July OTA - now getting 'Device is Corrupt" error

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