Previous commenter gets “Cannot modify header information” error

Hi, I am working on setting up my first WordPress site (using 2.0 RC1).

When submitting a comment, if the user has a previous comment and is not an administrator, they get the following errors:

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Warning: strpos() [function.strpos]: Empty delimiter. in /home/c0dy10/public_html/wp-includes/comment-functions.php on line 867

Warning: Cannot modify header information – headers already sent by (output started at /home/c0dy10/public_html/wp-includes/comment-functions.php:867) in /home/c0dy10/public_html/wp-comments-post.php on line 54

Warning: Cannot modify header information – headers already sent by (output started at /home/c0dy10/public_html/wp-includes/comment-functions.php:867) in /home/c0dy10/public_html/wp-comments-post.php on line 55

Warning: Cannot modify header information – headers already sent by (output started at /home/c0dy10/public_html/wp-includes/comment-functions.php:867) in /home/c0dy10/public_html/wp-comments-post.php on line 56

Warning: Cannot modify header information – headers already sent by (output started at /home/c0dy10/public_html/wp-includes/comment-functions.php:867) in /home/c0dy10/public_html/wp-includes/pluggable-functions.php on line 178
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The comment is entered correctly, the redirect breaks.

I have not modified the three files referenced. To be absolutely sure, I redownloaded them and uploaded them – same problem.

In fact, I have only modified one file outside of templates, and that is kses.php, and just to be sure, I tried replacing that with a stock one and the problem still occurs.

Any help would be awesome.