Outlook 2007 intermittently prompting for credentials for E2k3 clu

[Socrates]

Have Outlook 2007 SP1 with the Jan 2008 rollup on Vista SP1 talking to
Exchange 2003 SP2. All users, workstations and servers are in the same
Windows Server 2003 native mode domain.

A number of users are intermittently being prompted for credentials in
Outlook 2007. The credential prompt contains the name of the Exchange 2003
cluster as the domain, not the Active Directory domain they are a member of.
Consequently no credentials entered in this box will dismiss it.

The prompt appears randomly, and not everyone experiences it. However
people that do have the issue always see it if the Exchange cluster is failed
over (although they experience it at other times too).

If credentials are entered into the logon prompt, a capture of network
traffic shows Outlook trying to open an RPC connection to Exchange, but
failing due to the supplied NTLM credentials not working.

-Has anyone has this issue before?
-Why am I not seeing Kerberos authentication traffic instead of NTLM
(despite the user having valid Kerberos tickets for Exchange - viewed via
Klist)
-Why does the credetial prompt contain the wrong domain (the Exchange
cluster name instead of the AD domain)


Thanks in advance.

 

[Socrates]

PS: I'm not using RPC over HTTPS - this is a direct connection; Cached mode
is not enabled.