emulator broken: This adb server's $ADB_VENDOR_KEYS is not set

Issue

Well a windows 10 update broke sleep, the computer went to sleep with the emulator open and now that's broken. When I run an app to launch in the emulator it will boot the emulator but won't install just time out. When I try and run an app into a running emulator instance Studio says:

com.android.ddmlib.AdbCommandRejectedException: device unauthorized.
This adb server's $ADB_VENDOR_KEYS is not set
Try 'adb kill-server' if that seems wrong.
Otherwise check for a confirmation dialog on your device.
Error while Installing APK

1. I've followed some of the other threads here. I've tried changing the environmental variable in control panel, but in fact I think it pointed to the right place originally, where the sdks are these days.
2. I've tried restarting the PC. I did try deleting a couple of adb files, that didn't work.
3. I've tried deleting all the sdks and downloading them again.
4. I've tried uninstalling and updating Android Studio, several times. Now on AS 3.1, still not working.

Bit of a nightmare really.

How do I set the vendor keys? Using AS console commands? Can anyone point me to a dummies guide, this is a bit of a tangent for me, wish I could fix it from the GUI.

Solution

OK so eventually downloading a nexus 4 x86 image android 27, with no play store worked. Sorry if this is repetition. Long live working emulators

Answered By - Sam