I was working on CSOM in SharePoint 2013 and suddenly when I
accessed the site I was getting the following error
Error:
The context has expired and can no longer be used. (Exception from HRESULT:
0x80090317)
This is because the security context of the session might be
expired. Please follow the following link to resolve this issue.
http://altaf-pinjari.blogspot.in/2011/04/error-context-has-expired-and-can-no.html
Site started working fine. Very useful.