SSRS 2008: Unable to restore encryption key

I have migrated SQL server 2005 database to sql server 2008 using side by side upgrade. I have copied Reportserver and reportservertempdb database across and configured SQl server Reporting services 2008 to use this new database. I am not able to restore SSRS key over to new SSRS 2008 server. The key restore reports:

Microsoft.ReportingServices.WmiProvider.WMIProviderException: An error occurred when attempting to connect to the report server remote procedure call (RPC) end point. Verify that the Report Server Windows service is running, and then retry the operation.

 ---> System.Runtime.InteropServices.COMException (0x800706B3): The RPC server is not listening. (Exception from HRESULT: 0x800706B3)
   --- End of inner exception stack trace ---
   at Microsoft.ReportingServices.WmiProvider.RSWmiAdmin.ThrowOnError(ManagementBaseObject mo)
   at Microsoft.ReportingServices.WmiProvider.RSWmiAdmin.RestoreEncryptionKey(Byte[] encryptedBytes, String password)
   at ReportServicesConfigUI.WMIProvider.RSReportServerAdmin.RestoreEncryptionKey(Byte[] encryptedBytes, String password)

I can open SSRS website but just not the encrypted content because of failure in restoring SSRS key.

Can anyone help please?

Late reply, but I just ran into this issue with moving SSRS 2008 R2 to a new server.

Had the same problem as described above, but going through the Database and Credentials wizards fixed it for me, even though I made no changes and everything was displayed correctly.

Go to Database -> Change Credentials/Change Database in the configuration manager and click through both wizards.

After that I was able to restore the keys.

What error do you get in Reporting Services Configuration Manager when you try and restore the encryption key through there?