Hey,
I found the problem. Something changed in joomla 1.6/1.7. This caused the parameters by menuitem to be unavailable. I found some other problems which i also fixed.
And then i needed to fix these problems in 4 other components i have made which are based on the same code. This means i was busy. I fixed all and updated the files and version numbers in the joomla extension directory.
You can now proceed to the download page and download Add user frontend version 1.2.8:
http://www.ghanja.be/en/downloads/components/add-user-frontend/details.html
With this version you will be able to configure the component based on the menu item. This means you can run different instances of the component using different parameters.
So if all is okay you should be able to do what i told you in my previous post.
grtz Kim