well did you run your upgrade for example if you upgraded from 8.0 to 8.11 there is an upgrade where as if you ran 8.1 there is not. based on the error your saying I would think you have not ran your upgrade which adds the usergroup captcha field which is why you can not get usergroup perms.
There are 3 xml files in the install directory the ones we note on the documentation.
Your correct action would be to upload all the files except the 2 config files and run the upgrades you where suppose to run. Once you do that follow the instructions for upgrade and go to your admin panel and generate the xml file and install it into vb
The only way your going to get an error on your forum is if the xml is not correctly permissioned so that it can be saved with your proper site info.
The documentation was extensively reworked with the series 8 to make it easier to follow telling you step by step what to do.