Comments submission has stopped working.

Hi all, first time poster, long time WP user.

I help out with a comic-book site for an artist friend (https://www.spaceavalanche.com), and the comments submission process has mysteriously stopped working since about 21 days ago (28th April 2011). The comments form posts to the wp-comments-post.php page, but no data is saved, and the URI is redirected to a location that references an error.

For example:
Posting a comment on https://www.spaceavalanche.com/2011/01/25/chinese-lantern/

..does not post and redirects to

https://www.spaceavalanche.com/2011/01/25/chinese-lantern/comment-page-2/?rcommentid=10557&rerror=htmllang%3Den&rchash=ca423fea170b6ad66ca79ddfa5ed34d2

Has anybody else seen this before? Can someone please shed any light?

We’re on WP 2.8.4 and are reluctant to upgrade just yet as some plugins being used are not covered in the later versions of WP.

All input appreciated, it would be great if someone could help out.

Cheers,
WoolyG