I have the following running, Exchange 2007 SP1 installed on W2k8 as a virtual machine running on a W2k8 Hyper-V on a HP DL360, in an existing W2k3 child domain with Exchange 2003 SP2 on a W2k3 SP2 server, all DCs and GCs are W2k3 SP2. Installation went OK. New user accounts created with EMC on Exchange 07 server are able to login and send/receive email with other users, internal and external. The problem, when I use EMC I can access all of the user account properties tabs except for the Account Tab, if I use W2k3 ADUC it works as expected. Using an Enterprise admin account makes no difference. EMC displays the following error and crashes and must be shutdown. Object reference not set to an instance of an object at Microsoft.Exchange.Management.SystemManager.UPNSuffixesDataTableLoader.IsTopLevelDomain(String domainFqdn) at Microsoft.Exchange.Management.SystemManager.UPNSuffixesDataTableLoader.AddDomainHierarchy(DataTable resultTable, ADObjectId domain) at Microsoft.Exchange.Management.SystemManager.UPNSuffixesDataTableLoader.OnRefreshCompleted(RunWorkerCompletedEventArgs e) at Microsoft.Exchange.Management.SnapIn.Esm.Recipients.MailboxAccountPropertyControl.OnSetActive(EventArgs e) at Microsoft.Exchange.Management.SystemManager.WinForms.ExchangePage.OnSetActive() at Microsoft.Exchange.Management.SnapIn.ExchangePropertyPage.OnSetActive() at Microsoft.ManagementConsole.SnapInBase.ProcessNotification(Notification notification) at Microsoft.ManagementConsole.Internal.SnapInClient.Microsoft.ManagementConsole.Internal.IMessageClient.ProcessNotification(Notification notification) at Microsoft.ManagementConsole.Internal.IMessageClient.ProcessNotification(Notification notification) at Microsoft.ManagementConsole.Executive.SnapInNotificationOperation.ProcessNotification() at Microsoft.ManagementConsole.Executive.Operation.OnThreadTransfer(SimpleOperationCallback callback) Any ideas?

I am experiencing the same problem on a XP Client machine with the Exchange management console installed. Fortunately I'm not experiencing this behaviour on the production servers. I tried uninstalling .net Framework 1.1, installed .net Framework 3.0, still the same problem. I'll let you know if I find a solution.