You can either try going back to .15 using a blob file root and use ota root keeper from the market to keep your root and ota back to .21 or you can unlock your device install a custom recovery and flash a pre rooted rom. Heres a link for the blob method xda-developers - View Single Post - Wolf's ultimate flash and downgrade guide (NO ROOT NEEDED) (root opportunity for .21)
I'll try that. Thanks!
It worked! Big thanks ^^