The URL ‘[url]‘ is invalid. It may refer to a nonexistent file or folder, or refer to a valid file or folder that is not in the current Web in SharePoint

My Work Env:

 I got the error "The URL ‘[url]‘ is invalid. It may refer to a nonexistent file or folder, or refer to a valid file or folder that is not in the current Web"  in SharePoint 2010. The site was working fine, but after few days the SharePoint site got the error.

    In my scenario, the lookup filed does not give this error, because i don't use any lookup field in SP env.
(for ref : http://bernado-nguyen-hoan.com/2011/03/22/sharepoint-evil-1-the-url-url-is-invalid-it-may-refer-to-a-nonexistent-file-or-folder-or-refer-to-a-valid-file-or-folder-that-is-not-in-the-current-web/ ).

  Root Cause:
   My SharePoint site's DB machine has 0bytes free memory.

Solution:
   I freed some space, then site works as normal.