"Something went wrong" when you access a site

Symptoms

When you try to access a Microsoft SharePoint 2013 website, you receive the following error message:

Sorry, something went wrong
An unexpected error has occurred.

Also, the following error entry is logged in the ULS log:

 Application error when access /, Error=Exception of type 'System.ArgumentException' was thrown.  Parameter name: encodedValue  
 at Microsoft.SharePoint.Administration.Claims.SPClaimEncodingManager.DecodeClaimFromFormsSuffix(String encodedValue)  
 at Microsoft.SharePoint.Administration.Claims.SPClaimProviderManager.GetProviderUserKey(IClaimsIdentity claimsIdentity, String encodedIdentityClaimSuffix)  
 at Microsoft.SharePoint.Administration.Claims.SPClaimProviderManager.GetProviderUserKey(String encodedIdentityClaimSuffix)  
 at Microsoft.SharePoint.Utilities.SPUtility.GetFullUserKeyFromLoginName(String loginName)  
 at Microsoft.SharePoint.ApplicationRuntime.SPHeaderManager.AddIsapiHeaders(HttpContext context, String encodedUrl, NameValueCollection headers)  
 at Microsoft.SharePoint.ApplicationRuntime.SPRequestModule.PreRequestExecuteAppHandler(Object oSender, EventArgs ea)  
 at System.Web.HttpApplication.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()  
 at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)     

Cause

This issue occurs if a Group Policy setting that is applied to the SharePoint server removes the IIS_IUSRS group from the Impersonate a client after authentication local security policy.

Resolution

To fix the issue, follow these steps:

1. On the SharePoint server, type secpol.msc in the Run dialog box, and then press Enter to open the Local Security Policy console.
2. Under Security Settings, expand Local Policies, and then click User Rights Assignment.
3. In the details pane, double-click Impersonate a client after authentication.
4. Click Add User or Group, add IIS_IUSRS, and then click OK two times to close the dialog box.

More information

Still need help? Go to SharePoint Community.