HI There, I am trying to install an Exchange 2010 server into an existing Exchange 2007 environment. The prerequisites have been met and the installation seemed to be running fine. It failed during the Hub transport installation with a permissions error. This was linked to a certificate not being in the Trusted root certificate authorities store which I have corrected. The hub transport role did not complete successfully. Now when I start the setup again it starts in maintenance mode and does not allow me to complete the hub transport installation (the checkbox is greyed out) and attempts to continue installing the CAS and Mailbox Role. The following error is now encountered when continuing the installation: Summary: 3 item(s). 1 succeeded, 1 failed. Elapsed time: 00:00:02 Preparing Setup Completed Elapsed Time: 00:00:01 Client Access Role Failed Error: The following error was generated when "$error.Clear(); $thisServer = Get-ExchangeServer $RoleFqdnOrName; $adSiteId = $thisServer.Site; $pureMailboxServersFqdns = Get-ExchangeServer | Where {$adSiteId -eq $_.Site -and $_.IsMailboxServer -and -not $_.IsClientAccessServer} | ForEach {$_.Fqdn}; Get-MailboxDatabase | Where { ($pureMailboxServersFqdns -contains $_.RpcClientAccessServer) -and ($adSiteId -eq (Get-ExchangeServer $_.Server).Site)} | Set-MailboxDatabase -RpcClientAccessServer $thisServer" was run: "Value cannot be null. Parameter name: key". Value cannot be null. Parameter name: key Elapsed Time: 00:00:01 Finalizing Setup Cancelled Any ideas on this would be greatly appreciated. Thanks, Steven

Check this out http://social.technet.microsoft.com/Forums/en-US/exchange2010/thread/989138b4-8543-48db-b042-f689d1bf60b6/ Gulab | MCITP: Exchange 2010-2007 | Skype: Gulab.Mallah | Blog: www.ExchangeRanger.blogspot.com