Yes, sure. The thing is that when you add a user to a group, you don't modify the user, you modify the group. You add the user's Distinguished Name (DN) to the Member property of the group. The Member Of property of the user is updated automatically by Active Directory, and Active Directory does not allow anyone update the property.
Also, you cannot add the user to a group before a user is created. When a user is not yet created, he/she does not yet have a Distinguished Name. That is, there is yet nothing to store in the Member property of the group.
In the Web Interface forms that are used for viewing/editing users, the Member Of section (not property) is used to update the user's membership in group. That section was especially designed to allow adding/removing users from groups directly from the pages for viewing/editing users. That section updates the Member property of the group that you add the user to. But as we've already mentioned above, this approach cannot be used as the new user does not yet have a DN that can be added to the Member property of the group.
To workaround this, you can add newly created users to groups automatically with a Business Rule triggered after creating a user. For example, take a look at the following tutorial that describes how to accomplish the task: http://www.adaxes.com/tutorials_Automat ... rtment.htm .
Alternatively, we can suggest the following approach: you can add one more text field to the form for creating users. For this purpose you can use one of Adaxes virtual properties, for example, CustomAttributeText1. In that field you can specify the name(s) of the group(s) the newly created user should be added to. Then, you can create a Business Rule triggered after creating a user that will use a PowerShell script to read the group name(s) stored in the virtual property and add the user to the specified groups. The only drawback of the method is that you will have to type in the groups manually, there won't be a window to select/browse for groups. If you are interested in such a solution, we will provide more details.