Facebook Connect Return URL generating a 404

Im currently setting up a new site which uses CodeIgniter and the Facebook library created by Elliot Haughin.

Whenever I got to login, it goes off to Facebook to authenticate then returns with this URL:

http://mydomain/?code=wu8doZh9J-L5cN_2srlAETjJA3Myiv0QnozhkfePC0M.eyJpdiI6InhRMjZGcU1xcDM0NmtUaWtyTF9seXcifQ.RTjdoA95sZ_YmDAj84qSjKo3eLB489sA0hvzDBRWgIUa开发者_如何学JAVA7LBvm4SSVv9fNOpgAJmRKyLxLpBExsGr_McMX-LR8Jl23LfTB839UVihGChBnTbOyNXnnfT0M_laqVXdUi2doNtRNBvcUzBb7F54D7VSo

This in turn gives me CodeIgniter's standard 404 page. Even though I have a .htaccess file set up which should be sending all 404's to the index.php?

Do you have config parameter

$config['uri_protocol']

$config['permitted_uri_chars'] = '?=&a-z 0-9~%.:_-';