Unable to back up the SQL Server Reporting Services encryption key for MSD ax 2012 R3

Solution on below error

Problem and Error

Reporting extension installation error for ax 2012 R3.
Verifying the credentials for the Microsoft Dynamics AX .NET Business Connector proxy.
Back up the SQL Server Reporting Services encryption key.
The reporting server is not set up correctly, and cannot be configured by Setup. For information about setting up a reporting server, see SQL Server Books Online.
An error occurred during setup of Reporting Services extensions.
Reason: Unable to back up the SQL Server Reporting Services encryption key. The operation failed with error code 2147944645.
System.InvalidOperationException: Unable to back up the SQL Server Reporting Services encryption key. The operation failed with error code 2147944645.
at Microsoft.Dynamics.Setup.IdentityUpdater.<SetServiceAccount>b__2(ErrorCodes code)
at Microsoft.Dynamics.Setup.IdentityUpdater.CheckHresult(Int32 hresult, Action`1 exceptionAction)
at Microsoft.Dynamics.Setup.IdentityUpdater.SetServiceAccount(SrsWmi rsconfigSetting, String userName, String password)
at Microsoft.Dynamics.Setup.IdentityUpdater.UpdateSRS(SrsWmi rsconfigSetting, String userName, SecureString password)
at Microsoft.Dynamics.Setup.ReportsServerInstaller.SetInstanceIdentity(String instanceName, String sharePointServiceApplicationSite, String username, SecureString password)
at Microsoft.Dynamics.Setup.Components.ReportingServicesExtensions.SetInstanceIdentity(String instanceName, String sharePointServiceApplicationSite, String userName, SecureString password)
at Microsoft.Dynamics.Setup.Components.ReportingServicesExtensions.RunReportingSetupManagerDeploy()
An error occurred during installation of the Microsoft Dynamics AX Reporting Services extensions. See the installation log for details.
Registering tracing manifest file "C:\Program

Solution:
1.Delete the .auc files and and registry key by command prompt.
2. The length of password while taking the backup of sql reporting encryption key should match with password policy length.if password policy length is 10 then the password while giving for encryption key length should be 10.otherwise it will throw the above error.
3. The account which we are using for reporting service extension password length should match with password policy length.
4. If still error exists then  uninstall the reporting extension and Sql reporting service  and re-install the same.
5.Try to reinstall reporting extension without configuration of reporting service it not success then configure one by one tab.
6. Take backup of encryption file at last and restore it.
7. Try to install reporting extension again if its installed with warning then try to deploy one report if its ok then you can proceed for other report deployment.