Save Template Error - No Windows Identity for DOMAIN\User

When trying to save a template today I encountered an error, I never had an issue saving templates before so I had a look in the logs to check what was causing it. In the logs I found the following error:

SPSecurityContext.WindowsIdentity: Could not retrieve a valid windows identity for NTName='DOMAIN\User', UPN='User@domain.com'. UPN is required when Kerberos constrained delegation is used. Exception: System.ServiceModel.FaultException`1[System.ServiceModel.ExceptionDetail]: WTS0003: The caller is not authorized to access the service. (Fault Detail is equal to An ExceptionDetail, likely created by IncludeExceptionDetailInFaults=true, whose value is: System.UnauthorizedAccessException: WTS0003: The caller is not authorized to access the service.    at Microsoft.IdentityModel.WindowsTokenService.CallerSecurity.CheckCaller(WindowsIdentity callerIdentity)     at Microsoft.IdentityModel.WindowsTokenService.S4UServiceContract.PerformLogon(Func`1 logonOperation, Int32 pid)     at SyncInvokeUpnLogon(Object , Object[] , Object[] )     at System.ServiceModel.Dispatcher.SyncMethodInvoker.Invoke(Object instance, Object[] inputs, Object[]& outputs)     at System.ServiceModel.Dispatcher.DispatchOperationRuntime.InvokeBegin(MessageRpc& rpc)     at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage5(MessageRpc& rpc)     at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage4(MessageRpc& rpc)     at System.ServiceModel.Dispatcher.MessageRpc.Process(Boolean isOperationContextSet))

Claims Authentication  No windows identity for domain\user.

Looking online gave me no answers until I came across this blog by Doug Ware which talked about a change made by KB979917.

In the Application Settings for my Sharepoint Site I changed the aspnet:AllowAnonymousImpersonation to false and then performed an iisreset (beware that this will cause disruptions to your sharepoint website so either take the servers out of the load balancer one at a time or organise downtime).

After that I tried to save a site as a template and got a rather pleasing Operation Completed Successfully.

On my UAT environment I got a further error:

VtemplateManager::loadUncustomizedFormSchema failed with error code 0x80004005.    a93fecf5-fef9-4498-ae66-569b5872f930

CFormWebPartXmlFromRowSetData::Parse failed with 0x80004005    a93fecf5-fef9-4498-ae66-569b5872f930

CWebPartXmlBuilder::Add failed with 0x80004005    a93fecf5-fef9-4498-ae66-569b5872f930

Cannot complete this action.  Please try again.    a93fecf5-fef9-4498-ae66-569b5872f930

Which I fixed by running the script in my post about fixing broken discussion boards. After running the script I tried to save the template and it completed successfully.