Please refer to question Q_20913274.html. for more background on this situation.
Some of our Outlook clients started receiving this message(s) when starting up Outlook. We went through all the usual troubleshooting steps involving network connectivity, name resolution, rpc ping, nslookups, checked the DNS entries as well as WINs entries. No trouble was found in any of those tests, with the exception of pinging the host name of the Exchange server. That failed. Pinging the qualified name worked. I added the Exchange server and a couple of Global Catalog servers to the Host file and the issue was "resolved". Further, we discovered that a better solution was to remove "ncacn_np" from the string on the [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Exchange\Exchange Provider] "Rpc_Binding_Order.
The question is: What happened? Why was it working the day before and not now? and if it is a DNS problem why isn't everyone having the same problem? We only have 2 DNS servers. The first is a primary which does a zone transfer to the second. It doesn't make sense that an event happened that effected random clients. It would be logical that something changed at a single point of failure, like maybe the DNS server, or the Exchange server(s) but if that were the case it would affect the entire domain. BTW, the mailboxes are distributed across 11 Exchange servers and the problem happened with clients on all 11. Any ideas?
P.S. The client versions range from Outlook 98 to Outlook 2003. The OS's from NT4 to XP Pro service pack 2 with all up to date patches. The Exchange servers are 2003. We have not had any problems to date with the 2003 clients.