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We have a problem that just came up out of the blue with Google, in particular Webmaster Tools & our Merchant Center.  We're getting a 404 errors for 1000s of pages in both of these applications, but the pages are working just fine.  Our shopping campaigns have been hit hard as many of our top products have been suspended from our merchant feed.  Webmaster tools is giving us 1000s of 404 errors to product & category pages alike. But every page returning a 404 error is working.  We've contacted Google and they mention that they are not getting a 404 error, but their crawler seems to be.  Has anyone ever experienced this?  What could be causing this? Thanks for any input.