"File not found" if redirecting with a .php url.

After updating our site, I created a bunch of redirects from pages that used to exist on the old site to the pages on the new site. I'm finding that anything with the extention .php will not redirect. Instead, I get a white page with "File not found".

For example:
From: example.php (which does not exist)
To: redirect-example (a node that does exists)

Please help.