Thread:Talk:Extension default namespaces/Please define a serious range for user/reply (6)

That "Invalid or virtual namespace" error message has nothing to do with custom namespace numbers - it's an error brought about by a combination of certain versions of ConfirmEdit (maybe the ones that come with MW 124 and MW 1.25) and Semantic Forms. I'm hoping to be able to find a patch to fix it; though I think with the very latest version of ConfirmEdit, it's no longer a problem.