Why would SEOMoz and GWT report 404 errors for pages that are not 404ing?

[secretstache]

Recently, I've noticed that nearly all of the 404 errors (not soft 404) reported in GWT actually resolve to a legitimate page.  This was weird, but I thought it might just be old info, so I would go through the process of checking and "mark as fixed" as necessary.  However, I noticed that SEOMoz is picking up on these 404 errors in the diagnostics of the site as well, and now I'm concerned with what the problem could be.

Anyone have any insight into this?

Rich

[PracticeFusion]

Hi Rich,

Are you willing to post some of the URLs here so that we can take a look?

Phil

[secretstache]

Hey Phil, Thanks for the response.  Here are a few links considered 404's in GWT:

// A WordPress Attachment Page that redirects up to the parent post

http://windells.com/2012/snowboard/windells-snowboard-camp-breeds-champions-in-oslo/attachment/champions_mens_slopestyle_prizes__photo_oystein_kvanneid_2/

// An old page that is redirected to the new page

http://windells.com/sports/snowboard/

[PracticeFusion]

Hey Rich,

Unfortunately, I only have one suggestion for you.

Throw your supposed 404 URLs into this tool http://www.tomanthony.co.uk/tools/bulk-http-header-compare/

This will allow you to check their response codes in real time to erase all doubt of whether they're 404ing or not.

[secretstache]

Ok, so now I'm seeing a real problem because the tool you provided is confirming that it is a 404, but the page IS redirecting.

Can this be because of the aggressive caching I have setup with my webhost?

Rich