When a user registers through the API or directly through the forum, the Real_Name field is set even if it is blank, so the Real_Name field in the database should not contain a Null value.
It should either have the persons input (their real name), or be blank, it should not have a Null value.
The next version of Web Wiz Forums, which will be 10.04 will have version 2.0 of the XML HTTP API and will add to the 'todo' list a test for Null values in the Real_Name to avoid this issue.
If you currently have support then you can fill out a support ticket from your Client Area account and we can look in to this further for you and see if can fix the issue for you.