Error with cu6 installation

Hello ,

how can i know which cu !!! installed on my exchange ? from where can i know the cu version installed ?

also i am trying to install exchange cu6 in one of my customer and it give me the below error 

Error:

The following error was generated when "$error.Clear();

          $maxWait = New-TimeSpan -Minutes 8

          $timeout = Get-Date;

          $timeout = $timeout.Add($maxWait);

          $currTime = Get-Date;

          $successfullySetConfigDC = $false;

          while($currTime -le $timeout)

          {

            $setSharedCDCErrors = @();

            try

            {

              Set-SharedConfigDC -DomainController $RoleDomainController -ErrorVariable setSharedCDCErrors -ErrorAction SilentlyContinue;

              $successfullySetConfigDC = ($setSharedCDCErrors.Count -eq 0);

              if($successfullySetConfigDC)

              {

                break;

              }

              Write-ExchangeSetupLog -Info ("An error ocurred while setting shared config DC. Error: " + $setSharedCDCErrors[0]);

            }

            catch

            {

              Write-ExchangeSetupLog -Info ("An exception ocurred while setting shared config DC. Exception: " + $_.Exception.Message);

            }

            Write-ExchangeSetupLog -Info ("Waiting 30 seconds before attempting again.");

            Start-Sleep -Seconds 30;

            $currTime = Get-Date;

          }

          if( -not $successfullySetConfigDC)

          {

            Write-ExchangeSetupLog -Error "Unable to set shared config DC.";

          }

        " was run: "System.Exception: Unable to set shared config DC.

   at Microsoft.Exchange.Configuration.Tasks.Task.WriteError(Exception exception, ErrorCategory category, Object target, Boolean reThrow, String helpUrl)

   at Microsoft.Exchange.Configuration.Tasks.Task.WriteError(Exception exception, ErrorCategory category, Object target)

   at Microsoft.Exchange.Management.Deployment.WriteExchangeSetupLog.InternalProcessRecord()

   at Microsoft.Exchange.Configuration.Tasks.Task.<ProcessRecord>b__b()

   at Microsoft.Exchange.Configuration.Tasks.Task.InvokeRetryableFunc(String funcName, Action func, Boolean terminatePipelineIfFailed)"

How can i solve this issue .

I have 2 cas servers and 2 MBX server

cu6 successfully installed in Cas1 but others not

schema prepared already

need help please