Yep, that's it. Thanks Ray.
On that basis, shouldn't the page refresh itself and present the errors? Currently it's going to the home page with the ?invalid=true.
I'm asking because as the person building the site, I wasn't aware of the error and therefore any normal user isn't going to know.
I've resolved it at the moment by adding in registration.php before the ?invalid=true, but was wondering if that wasn't how it's intended to work.
Also, the error message contains @@strengthmessage@@ and was wondering if that is meant to be dynamic in some way referencing code elsewhere pertaining to the minimum limit of characters, or if it was simply there to remind us that we need to change it manually?