recently I have changed the Tridion Application Pool User to domain user.
When I try to grant on RSA KEY I obtain the next error:

c:\Windows\Microsoft.NET\Framework64\v4.0.30319>aspnet\_regiis -PA "TridionRsaKey
Container" "domain\username"

Microsoft (R) ASP.NET RegIIS version 4.0.30319.34209
Administration utility to install and uninstall ASP.NET on the local machine.
Copyright (C) Microsoft Corporation. All rights reserved.
Adding ACL for access to the RSA Key container...
No mapping between account names and security IDs was done. (Exception from HRES
ULT: 0x80070534)
Failed!

Could any helps me please?
Thanks!