Powershell Remote: Microsoft.Update.Session, Access Denied: 0x80070005

This is a known issue. It appears that there is a bug with the actual COM object itself, as this issue occurs when using VBScript, PowerShell, and even C#. There is a good article that discusses managing Windows Update with PowerShell that can be found here.

The workaround is to set up a scheduled task on the computer and you can invoke that task however you see fit.

Use PsExec (http://technet.microsoft.com/en-us/sysinternals/bb897553.aspx) to remotely execute PowerShell with a script file:

psexec -s \\remote-server-name C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe \\server\script.ps1

I used the script detailed at http://www.ehow.com/how_8724332_use-powershell-run-windows-updates.html, and I can remotely execute it using psexec to download and install updates.