I will try to explain the situation:
In December 2012 I deployed a website with a sitemap.xml, etc... there were circa 2000 URLs.
After a while I changed something on my website, upgrading my pages to circa 30,000 and I deployed again updating the sitemap.xml.
I also updated the routing of my urls: ie: from
Now for some reason I'm receiving from Google Webmaster Tools 8 crawl errors with a 500 status code on some pages with an old URL... how can it be possible? And how can I fix it?