Comment Submit displays: wp-comments-post.php

As the topic says: I have a few blogs that I manage for others. I am running the latest version of WordPress but recently there has been this strange error when people are trying to post comments.

Post displayed OK – comment filled and on clicking the submit button the reader is displayed the /wp-comments-post.php which of course is blank. No error nothing – just a blank browser page.

This only happens with some posts and not others, no reason or commonality that I can see. I have tried redoing the post with a different title – same error. I have tried disabling plugins – no effect.

I have searched in the forums and can’t find anything. So any help or assistance would be appreciated.

Regards