can't open new powershell session from one server to another

I am trying to open a powershell session from one server to another. I can open sessions to servert1/2 which have the same configuration as far as I can tell. trustedhosts are the same, same user/pw being used. Yet when trying to open a session to serverp01 I get the following error:

Enter-PSSession : Connecting to remote server serverp01 failed with the following error message : WinRM cannot process
the request. The following error with errorcode 0x80090322 occurred while using Kerberos authentication: An unknown
security error occurred.
 Possible causes are:
  -The user name or password specified are invalid.
  -Kerberos is used when no authentication method and no user name are specified.
  -Kerberos accepts domain user names, but not local user names.
  -The Service Principal Name (SPN) for the remote computer name and port does not exist.
  -The client and remote computers are in different domains and there is no trust between the two domains.
 After checking for the above issues, try the following:
  -Check the Event Viewer for events related to authentication.
  -Change the authentication method; add the destination computer to the WinRM TrustedHosts configuration setting or
use HTTPS transport.
 Note that computers in the TrustedHosts list might not be authenticated.
   -For more information about WinRM configuration, run the following command: winrm help config. For more
information, see the about_Remote_Troubleshooting Help topic.
At line:1 char:1
+ Enter-PSSession
+ ~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidArgument: (serverp01:String) [Enter-PSSession], PSRemotingTransportException
    + FullyQualifiedErrorId : CreateRemoteRunspaceFailed

See below from here: https://social.technet.microsoft.com/Forums/windows/en-US/a4c5c787-ea65-4150-8d16-2a19c569a589/enterpssession-winrm-cannot-process-the-request-kerberos-authentication-error-0x80090322?forum=winserverpowershell

Hi Sergey, In my opinion, it's possible that the existing HTTP/SERVERNAME SPN registered under the domain account is related the error. Please try the action below: 1. On the server, change IIS application pool to run under Local System. 2. Run the following commands to remove existing SPN: setspn -D HTTP/SERVERNAME setspn -D HTTP/SERVERNAME.DOMAINAME.COM 3. Then connect to the server again to see what will happen. If the issue remains, disable Kernel mode authentication in IIS management console. Regards, Diana