Last week I had a script which generated popup during my task sequence. This popup was visible behind the task sequence progress window. I searched for a solution to hide the task sequence progress window and found a post from Michael Niehaus on the TechNet blogs. The link to the original post is:
 The proposed solution was written in VBScript. My script was written in PowerShell so I created a PowerShell version of the script for hiding the progress window during the task sequence. The script below will hide the task sequence progress window until it continue with the next task.
#Hide the progress dialog $TSProgressUI = new-object -comobject Microsoft.SMS.TSProgressUI $TSProgressUI.CloseProgressDialog()