VQmod extension for 2.0 wont work in 2.1

Hello

Ive upgraded my shop to version 2.1.02 from 2.0 and had a module for username login.
when I upgraded it stopped working and the developer has only version for 2.0

It is this module(all VQmod)
http://www.opencart.com/index.php?route ... h=username

Are there any out there that can help me to explain what the big different in 2.0 and 2.1 are in the code so I can change it to work. or anyone that will help me do it?¨

Thanks /Richard

Major change is that serialized replaced by json.
May be you can start check all extension code related to user_group database table.

For other change, you can check here

Thanks!!