My server went down for a couple days.(2-3 august)
15 days later, Google Webmaster Tools notified me of increase in 404 errors.
The problem is that Google reports 70,000 error pages while it has ever indexed maximum 7000 pages, as shows the index status:
While this is the crawl error page:
How can I understand which pages Google cannot find? I can see maximum 1000 errors but these 1000 errors are old and were present before too. And how is that possible that it cannot find 70,000 pages if it had ever indexed maximum 7000?
Note I have tried to run Xenu link checker to check for internal broken links and none were found.
Note2: In correspondence with the spike in errors (21th august) there were a spike in crawled pages too: