I too have had problems with people being able to register.
I think I have found the problem. - and the solution but it needs to be verified...
I have a site with 1200 users and about 6-10 new registrations each week. .... studentloans are hell in canada! My site helps people with these problems.
I think this is the problem....
If a user registers and turns on the "automatically log me in" but then forgets to activate, and then reregisters under a different name, and then tries to activate, they cant.
Or if they try to register and their cookie settings arent correct, and the registration fails, and then try to re-register under a different name then above happens too...
I suspect the "automatically log me in" creates a cookie on registration, but then when they return to the forum... WWF searches for a cookie for username and password, but the login would fail... and if they re-register then the cookie has the older username and password .
I would need to look more deeply into the source code to see when the cookie is being created.. but this seems to be the common scenario that causes the registration problem for a select number of registrants. 98% of registrations happen ok...
Having the user delete all cookies on their machine seems to clear up the problem.
This might also be a problem as a result of people trying to register from a public computer where the cookie is set and not cleared...not quite sure about this though....
I could be totally off the mark on this but it seems to be the only pattern I can think of... in each case, deleting cookies resolved the inability to register and activate.
Mark