301 in place, still many 404 in GWT. Why?

[gerardoH]

We have redesigned a website. The old site used to have lots of urls, the new sites has far less. We have pointed all old urls to the new urls with 301 redirects. This happened a couple of weeks ago. But we are still getting many 404 errors in Google Webmaster Tools.

What's the reason for this?

Thanks in advance.

[gerardoH]

Thanks for your reply, I'll follow your advice and keep you updated.

[gerardoH]

Hi Nicholas,

Thanks for taking the time to reply to our question.

1. GWT hasn't re-crawled since 301 implementation

Has re-crawled several times.

2. The 301ing URLs aren't all right

We will check this...

3. You're 301ing to 404'ing URLs.

No we're not.

4. About 100 other things.

Ok

[Copstead]

I would follow the urls that GWT say are bad.  This will give you the answers.  Also, for all bad urls, make sure you have GWT re-crawl them."Fetch as Googlebot" and "Submit to Index" under "Diagnostics"

[MRCSearch]

There are many potential reasons.

1. GWT hasn't re-crawled since 301 implementation

2. The 301ing URLs aren't all right

3. You're 301ing to 404'ing URLs.

4. About 100 other things.

Can't give specifics without specifics.