Microsoft Exchange 2013 CU2 Update Fails on Mailbox Role:Mailbox Service Error - Exchange now unusable

Hi Guys

I recently tried upgrading our existing exchange 2013 CU1 in a test lab to CU2 unfortunately the installs fails on the following.

I'm not to sure where it is get held up or what the problem is. Any Suggestions or help would be greatly appreciated

Mailbox role: Mailbox Service

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]::DiscoveryManagement_InitInfo.WellKnownGuid;
          $dmRoleGroup = Get-RoleGroup -Identity $dmRoleGroupGuid -DomainController $RoleDomainController -ErrorAction:SilentlyContinue;
          if( $dmRoleGroup -ne $null )
          {
            trap [Exception]
            {
              Add-MailboxPermission $dismbx -User $dmRoleGroup.Name -AccessRights FullAccess -DomainController $RoleDomainController -ErrorAction SilentlyContinue;
              continue;
            }
            
            Add-MailboxPermission $dismbx -User $dmRoleGroup.Identity -AccessRights FullAccess -DomainController $RoleDomainController -WarningAction SilentlyContinue;
          }
          }
          }
          }
        " was run: "Specified cast is not valid.".

Thanks