Canonical not working? Getting duplicate title/meta in Google Webmaster Tools

I took a look in GWT and am seeing a ton of duplicate title tags and meta descriptions. For instance one GWT entry list 4 duplicates. When I look into the duplicates, into the page source, I see that they all include this canonical reference (substituting the domain name):

If I follow the link, http://www.whatever.com/index.php?main_page=product_info&products_id=1290, I get "page not found" on the website. However if I manually swap out the & for &, it works, as in:

http://www.whatever.com/index.php?main_page=product_info&products_id=1290

Is this what is causing the problem? If so how do I fix it? If not, then what next?

2 problems:

first, ignore the warnings, Google has the correct canonical reference and eventually they will get around to fixing webmaster tools.
second, you pulled the url out of the source of the page so it's ampersand is escaped, as it should be... it's essentially code, not "click able"

& = &

I'll check again. Am wonder though why I'm not getting email notifications on replies.