RSS feed broken?

The XML link on the main navigation seems to be invalid. Here's the output from w3c's feed validator:

http://validator.w3.org/feed/check.cgi?url=http%3A%2F%2Flambda-the-ultimate.org%2Frss.xml

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'fi'

this is a common problem when copying and pasting from Adobe PDFs into HTML textboxes (or any text destination). For whatever reason, 'fi' gets copied as a non-printing character and it makes XML and other data encodings choke.

Edit: PHP in particular can't handle this well, either. (We're using Drupal, which uses the PHP language).