$config['allowed_types'] txt files work log files do not

[eluser]Unknown[/eluser]
I can upload txt files, but not log files.

I have a web form which I've set

Code:

$config['allowed_types'] = 'log|txt';

I receive this error message (in the log file) when I try to POST a .log file :

ERROR - 2009-07-29 15:34:11 --> The filetype you are attempting to upload is not allowed.

When I POST the same file with a .txt file extension the POST works.

Am I missing something? where should I go from here?

Thanks