Error: "Unable to calculate clock skew:" when accessing an Exchange 2010 mailbox if RpcClientAcce (4336012)

"Unable to calculate clock skew:" when accessing an Exchange 2010 mailbox if RpcClientAccessServer is set to a CAS array using (Microsoft) Network Load Balancing (NLB).

An error similar to the following example can be observed in a WLOG file generated by the Exchange Store Manager (ESM) service:

09:09:01 DEBUG: GuessExchangeVersion returns 00000000,ExchangeVersion=2010
09:09:01 ERROR: Unable to calculate clock skew:
09:09:01 NetRemoteTOD(\\CAS_array_name):
09:09:01 [00000035] The network path was not found.

Unable to acquire time from Exchange Server using the NLB address.

Confirmation of this problem can be obtained by running the following command, from a command line on the Archive Manager services server(replace CASARRAY with the CAS array NETBIOS hostname):

NET TIME \\CASARRAY

The following error should be received:

System error 53 has occurred.

The network path was not found.

Performing the same test using the the hostname of an Exchange server that is a member of the NLB array will succeed however, e.g.:

NET TIME \\ExchangeServer

Current time at \\ExchangeServer is 11/1/2011 1:11 PM

The command completed successfully.

To correct the problem:

1. Check that any firewalls between the Archive Manager server and the NLB address are not blocking Server Message Block (SMB) traffic. This includes the Archive Manager server itself and the CAS array servers.
2. Ensure the NLB port range (port rules) allow the full port range.
3. Ensure the NLB interface on each CAS array server is bound to the SMB protocol (File and Printer Sharing).

For additional causes of the clock skew error please see SOL68127 and SOL55165