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I have the yoast canonical magento extension installed... so that should have taken care of all of the duplicate pages.

However, I'm still seeing it as being a issue from within my seomoz account.  Could it be that I have the canonical tag in place and the seomoz crawler got it wrong.

Or should I take it that this is actually a more serious issue and that my yoast canonical extension could be broken?

Thanks so much for your response Dean.

I've also got a magento store with a large amount of 302 redirects.  It looks like the majority of them are a compare product page or a add to wishlist page 302'ing to a enable cookies page.... is your problem similar to this?

Should I just have my developer change the 302's to 301's?