Request failed with HTTP status 401: Unauthorized. in SSRS

Hello All,

Suddenly all reports and datasources failing to load and throwing error "The request failed with HTTP status 401: Unauthorized".

Microsoft SQL Server Reporting Services Version 10.50.2550.0 
SQL Server: 2008 R2 Service Pack 2(10.50.4339.0)
SharePoint 2010 : 14.0.7149.5000

Error:
10/07/2016 12:11:14.44               w3wp.exe (0x1580)                                       0x22F8 SQL Server Reporting Services    SOAP Client Proxy                       0000     High       Exception encountered for SOAP method GetSystemProperties: System.Net.WebException: The request failed with HTTP status 401: Unauthorized.     at Microsoft.SqlServer.ReportingServices2010.RSConnection2010.SetConnectionProtocol()     at Microsoft.SqlServer.ReportingServices2010.RSConnection2010.SoapMethodWrapper`1.ExecuteMethod(Boolean setConnectionProtocol)

When i try to load the report or datasource getting 401 error. Also getting same error for the below actions too.
When i click on the "Reporting Services Site Settings" page from site settings.

when i try to create new datasource from the report library.

I have verified below  things.
1. SPN is set for Report Server, Database server and SharePoint servers.
2. In Central admin report server Authentication Mode is "Trusted Account"
3. Authentication Settings in reportserver config
<Authentication>
<AuthenticationTypes>
<RSWindowsNTLM/>
</AuthenticationTypes>
<EnableAuthPersistence>true</EnableAuthPersistence>
<RSWindowsExtendedProtectionLevel>Off</RSWindowsExtendedProtectionLevel>
<RSWindowsExtendedProtectionScenario>Proxy</RSWindowsExtendedProtectionScenario>
</Authentication>


If it is kerberos authinication problem not sure why i am getting error when i try to open "Reportign services site settings".

Could you please find the above all information and help to fix the error.

Thanks
Liakath

MD.Liakath ali