This may have already been fixed in a later version.
I was trying to sign up at http://qooxdoo.org
, which uses DokuWiki 2006-03-09. It wouldn't let me register a new account with the full name "T.J. Crowder" or "TJ Crowder"; the attempts failed with the error "Invalid full name". Both names are valid. (I would recommend being *VERY* careful about telling someone their name is not valid.) Eventually someone suggested taking out the dots might not be enough and it might even not like the full caps first name "TJ", and so I signed up with "Tj Crowder" -- and it worked. Fortunately, I was then able to edit my name on my account to be correct ("T.J. Crowder"), so the validation applied at signup is more strict (and less correct, in my view) than the later account editing.
Apologies if this is already fixed, they seem to be on an older version.
tj at crowder software dot com