4xx error in sitemaps

I just check out the google sitemap stats.. There were a few 4xx errors..

Just check out the screen shot..

Can someone please tell me the reason for the error and how i can rectify it?

Do the links work when you visit them? If so, then Google just had a problem when it tried to reach that link. If not, then Google will eventually stop trying to reach it since it's an invalid link.

Hello,

some URLs in the list have errors because of possible incorrectly configured CRRs:
forums/cat10
forums/cat37

You have links that should point to forums/ subfolder, but are located in the root instead. Please check your website - perhaps you have a broken links somewhere:
/automobiles/
/music/
/register.php
/sendmessage.php
etc.