Redirect after posting a comment

Please help… I am having trouble resolving the issue with posting the comments; a detailed explanation is as follows:

I am using php-cgi lines in the files, this is a fresh install of 2.9.2 and so I am using the default theme and no plugins. When I am logged in as an admin I can post the comments, but when someone else tries to comment, the error message displayed is “500 Internal Server”; the comment is being posted but the redirect to the post is not happening. However, when I go back to the post and refresh I see that the comment is posted. So I think it is the redirect(after commenting) to the post that is not happening.

Could someone please help with suggestions, so that I could redirect to the post after the comment is posted by someone who is not logged in. Thank you very much.