Sharepoint 2013 The context has expired and can no longer be used

I came across this odd error a couple of times in the past few weeks, so I wrote a quick guide that might help you get rid of it.
If you see this error after opening your SharePoint 2013 site, there is a lack of synchronization between Date and Time settings in your SharePoint 2013 Server and your SharePoint web application.
Sorry, something went wrong. The context has expired and can no longer be used. (Exception from HRESULT: 0×80090317)

Here is how you fix it!

• 
  
• Open Central Administration -> Application Management.
• Locate the relevant Web Application and click on 
• Web Application General Setting window will open up, notice that the Default Time Zone is missing.

Open Date and Time options on your server and check which time zone is configured. Configure the same time zone in Web Application General Setting.

Perform IIS Reset and open your SharePoint 2013 site again.

Hooray! SharePoint site works again!

Ref Link : http://blog.cloudshare.com/2012/10/22/how-to-fix-sharepoint-2013-web-application-error-the-context-has-expired-and-can-no-longer-be-used/#more-3508

Enable Anonymous Access to a SharePoint 2013 site

As is the case in previous versions, you can configure SharePoint 2013 sites to be accessed by anonymous users. In this article I will show the steps needed to configure anonymous access to an existing SharePoint 2013 site.
1. Navigate to the SharePoint 2013 Central Administration in your SharePoint 2013 environment. Under Application Management section, click the “Manage web applications” link.

2. Select one of the available web applications and press the “Authentication providers” button available in the Ribbon. A modal dialog showing the authentication providers available per zone is displayed. As you can see, in a basic scenario only the “Default” zone is listed.

3. Click the “Default” link so a new modal dialog is displayed. Just check the “Enable anonymous access” option and press the “Save” button

4. Navigate to one of the site collections you have created under the configured web application and go to “Configure -> Site Settings”. Under the “Users and permissions” section, click the “People and groups” link.

5. As you can see, SharePoint 2013’s Ribbon display is an “Anonymous Access” button that allows you to configure how anonymous users can access to the site.

6. Press the “Anonymous Access” button in the Ribbon so the related configuration modal dialog is shown. In this dialog you have three configuration options, just click the first one that provides full anonymous access to the site. Press the “OK” button.

7. Back to the “People and Groups” page, check there is a new group called “Anonymous users” available in the list.

8. We are almost done. To finish, start a new instance of a web browser and check that you don’t need to provide credentials information since anonymous access is enabled on the entire site.

And that’s all about how to enable anonymous access to a SharePoint 2013 site. I recommend you check out how it works in your SharePoint 2013 CloudShare environment.

Ref : link:-  https://support.cloudshare.com/entries/22231202-how-to-enable-anonymous-access-to-a-sharepoint-2013-site