Page Not Found?

I’m getting a number of reports that users click on links and don’t get where they should be taken:

Subject: A Concurrent Affair: Bad Link to
/blog/index.php/2006/09/19/local-variable-annotations/blog/index.php/
2006/09/19/local-variable-annotations/

A user tried to go to

http://www.concurrentaffair.org/blog/index.php/2006/09/19/local-variable-annotations/
blog/index.php/2006/09/19/local-variable-annotations/

and received a 404 (page not found) error.
It wasn’t the user’s fault, so try fixing it. The user came from

http://www.concurrentaffair.org/index.php/2006/09/19/
local-variable-annotations/

It looks like something with my permalinks or mod_rewrite is wrong, but I just can’t figure out what’s going on. If anyone notices this problem, could you please post a comment and describe what you were doing, i.e. what URL was displayed in your browser, what link you clicked on, and so on?

Thanks.