Exchange 2010 on Win2K8 Server fails

Currently installing Exchange 2010 on Win2K8 Server - current environment is Win2K3 domain running Exchange 2003 on Win2K3 Server - plan is to remove Ex 2003 Server once 2010 installed and tested.  Below is the latest in a line of errors encountered during installation - it's my first Exchange 2010 installation so any suggestions greatly appreciated.


Summary: 9 item(s). 7 succeeded, 1 failed.
Elapsed time: 00:09:00


Preparing Setup
Completed

Elapsed Time: 00:00:00


Stopping Services
Completed

Elapsed Time: 00:00:00


Copy Exchange Files
Completed

Elapsed Time: 00:00:02


Restoring services
Completed

Elapsed Time: 00:00:00


Hub Transport Role
Completed

Elapsed Time: 00:03:24


Client Access Role
Completed

Elapsed Time: 00:02:01


Unified Messaging Role
Completed

Elapsed Time: 00:00:44


Mailbox Role
Failed

Error:
The following error was generated when "$error.Clear();
          $name = [Microsoft.Exchange.Management.RecipientTasks.EnableMailbox]::DiscoveryMailboxUniqueName;
          $dispname = [Microsoft.Exchange.Management.RecipientTasks.EnableMailbox]::DiscoveryMailboxDisplayName;
          $dismbx = get-mailbox -Filter {name -eq $name} -IgnoreDefaultScope -resultSize 1;
          if( $dismbx -ne $null)
          {
            $srvname = $dismbx.ServerName;
            if( $dismbx.Database -ne $null -and $RoleFqdnOrName -like "$srvname.*" )
            {
              Write-ExchangeSetupLog -info "Setup DiscoverySearchMailbox Permission.";
              $mountedMdb = get-mailboxdatabase $dismbx.Database -status | where { $_.Mounted -eq $true };
              if( $mountedMdb -eq $null )
              {
                Write-ExchangeSetupLog -info "Mounting database before stamp DiscoverySearchMailbox Permission...";
                mount-database $dismbx.Database;
              }

              $mountedMdb = get-mailboxdatabase $dismbx.Database -status | where { $_.Mounted -eq $true };
              if( $mountedMdb -ne $null )
              {
                $dmRoleGroupGuid = [Microsoft.Exchange.Data.Directory.Management.RoleGroup]::DiscoveryManagementWkGuid;
                $dmRoleGroup = Get-RoleGroup -Identity $dmRoleGroupGuid -DomainController $RoleDomainController -ErrorAction:SilentlyContinue;
                if( $dmRoleGroup -ne $null )
                {
                  Add-MailboxPermission $dismbx -User $dmRoleGroup.Identity -AccessRights FullAccess -DomainController $RoleDomainController -WarningAction SilentlyContinue;
                }
              }
            }
          }
        " was run: "Couldn't resolve the user or group "hooperdolan.ie/Microsoft Exchange Security Groups/Discovery Management." If the user or group is a foreign forest principal, you must have either a two-way trust or an outgoing trust.".

Couldn't resolve the user or group "hooperdolan.ie/Microsoft Exchange Security Groups/Discovery Management." If the user or group is a foreign forest principal, you must have either a two-way trust or an outgoing trust.

The trust relationship between the primary domain and the trusted domain failed.

Click here for help... http://technet.microsoft.com/en-US/library/ms.exch.err.default(EXCHG.141).aspx?v=14.1.218.11&e=ms.exch.err.Ex88D115&l=0&cl=cp

Elapsed Time: 00:02:46


Finalizing Setup
Cancelled