I tried installing cyanogenmod on my samsung s2. I managed to sucessfully install cyanogen recovery on the device which boots up when I start the device.
After that I tried to install cyanogenmod which gets me an error:
adb push "cm-12.1-20160129-NIGHTLY-i9100.zip" /storage/sdcard0
error: 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.
I already tried to kill and restart adb server and also tried installing different usb drivers using Zadig.
I have read that USB debugging must be enabled on the device but the problem is that I cannot boot android anymore to set that option, I only get a start screen with a yellow exclamation mark and right after that cyanogenmod recovery menu shows up. Iam not sure if this option is the source of the problem, though.
Is the device bricked now or is there a way to either install cyanogenmod or at least restore the original android?
I now simply solved the problem by copying the cyanogenmod zip on the sdcard of another phone, then put this sdcard in my phone and then simply installing from sdcard via cyanogenmod recovery menu.