403 Forbidden when invoking emailafriend.php

I’ve recently started work for an organization that has a fairly mature WordPress publication – lots of articles go up each week, lots of people read them. I’ve never particularly done anything with WordPress before, but I seem to have the status in the office of Person Who Knows Computers (I’m an ex-Java-programmer :o) and there’s a problem with the WordPress installation which nobody seems to really care about, but I’d like to fix it!

Down the bottom of each article are three links – “Email a friend”, “News Alerts” and “Talk to us”.

The second two links work fine – they bring up a little popup box. The other one gives me this error:

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403 Forbidden
Access is forbidden to the requested page:

/wp-content/themes/revolution_news-21/readertoolbox/emailafriend.php (port 80)
Please forward this error screen to the WebMaster.

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I’m trying to look through the source code to see what could be going wrong – my first problem is that I don’t know what is calling what to end up at emailafriend.php. I can see in view source where it’s being called but if I go to Edit Themes I can’t see those lines in any of the php files, and there’s 40+ files there to dig through.

If I ftp in and poke around in the readertoolbox file then emailafriend.php is certainly _there_. It looks not particularly different from the php files for News Alerts and Talk To Us which work perfectly fine.

So I don’t really know where to go next to try to debug this. any help appreciated! I’m not really a php expert.