SCCM Client Push Error: Unable to access target machine for request

My customer called me for support due to client push failure. It is working fine the last time they performed client push. I checked out the ccm.log in the SCCM Primary Site, and I found majority failure is due to unable to access target machine for request. Back to the basics, I check the admin$ connection with one of the failure machine using windows explorer. It prompted for username and password, I entered the client push username and password. It doesn’t went through, and I entered again, and of course it failed again. Something wrong here, the client push account was granted with Domain Admin permissions. I asked my customer to enter another username and password that has the permission, and it went through. I suspected the Domain Admin permission was removed from the client push account, and asked the AD team to investigate. Yes, the Domain Admin permission was removed by someone. After the AD team configured back the Domain Admin permission, the client push is working fine. CHEERS!!!