CI mime types cause error with file upload

[eluser]charlie spider[/eluser]
just discovered that if i comment out:

Code:

'gif'    =>    'image/gif',
'jpeg'    =>    array('image/jpeg', 'image/pjpeg'),
'jpg'    =>    array('image/jpeg', 'image/pjpeg'),
'jpe'    =>    array('image/jpeg', 'image/pjpeg'),
'png'    =>    array('image/png', 'image/x-png'),

from the $mimes array then it works fine and allows me to upload a txt file !?!?!?

any ideas ?