Powershell Invoke-Command works when run manually, but not when in a script

I am building a script to remotely install the PSWindowsUpdate PowerShell module, open the correct firewall ports, and then run a command to install waiting updates. In order to install the PSWindowsUpdate module, I need to install an MSI on some of my machines to enable the "Install-Module" commandlet.

If I run the following code manually, in an admin PowerShell session on my local machine, it works fine:

$RemoteMachine = "DCSvrRDS16"
write-host "Server Name is: $RemoteMachine"

#Copy the MSI Local to the computer
Write-Host "Copying MSI locally"
Copy "\\dcsvrstorage2\software\microsoft\powershell\PackageManagement_x64.msi" \\$RemoteMachine\c$\

#Run the MSI remotely
Write-Host "Running MSI"
Invoke-Command -ComputerName $RemoteMachine -Credential $domaincredentials -ScriptBlock { c:\windows\system32\msiexec /i c:\PackageManagement_x64.msi /quiet /lvx* c:\PackageManagement.log } 4>&1

But if I run THIS full script IN THE EXACT SAME ALREADY OPEN PowerShell SESSION, the MSI does not install and the log file is not created:

Import-Module PSWindowsUpdate
$domaincredentials = Get-Credential


Function ProcessMachine($RemoteMachine) {

    write-host "Server Name is: $RemoteMachine"

    #Copy the MSI Local to the computer
    Write-Host "Copying MSI locally"
    Copy "\\dcsvrstorage2\software\microsoft\powershell\PackageManagement_x64.msi" \\$RemoteMachine\c$\

    #Run the MSI remotely
    Write-Host "Running MSI"
    Invoke-Command -ComputerName $RemoteMachine -Credential $domaincredentials -ScriptBlock { c:\windows\system32\msiexec /i c:\PackageManagement_x64.msi /quiet /lvx* c:\PackageManagement.log } 4>&1

    #Install the module
    Invoke-Command -ComputerName $RemoteMachine -Credential $domaincredentials -ScriptBlock { Install-Module PSWindowsUpdate -Force }

    #Turn on the firewall rules
    Invoke-Command -ComputerName $RemoteMachine -Credential $domaincredentials -ScriptBlock { Set-NetFirewallRule -DisplayName "COM+ Network Access (DCOM-In)" -Enabled True }
    Invoke-Command -ComputerName $RemoteMachine -Credential $domaincredentials -ScriptBlock { Set-NetFirewallRule -DisplayName "COM+ Remote Administration (DCOM-In)" -Enabled True }
    Invoke-Command -ComputerName $RemoteMachine -Credential $domaincredentials -ScriptBlock { Remove-NetFirewallRule -DisplayName "Remote WSUS Install" }
    Invoke-Command -ComputerName $RemoteMachine -Credential $domaincredentials -ScriptBlock { New-NetFirewallRule -DisplayName "Remote WSUS Install" -Profile Domain -Enabled True -Direction Inbound -Action Allow -Protocol TCP -LocalPort RPC }

    #Try the update
    Install-WindowsUpdate -ComputerName $RemoteMachine -AcceptAll
}

foreach ($machine in (Get-Content NeedsWSUS.txt)) {

    ProcessMachine $machine

}

It is driving me crazy. I have run ProcessMonitor on the remote machine, and I can see msiexec start and then stop without ever accessing the MSI in the root of the C: drive or trying to open the log file for write.

Has anyone seen anything similar? Client machine is Windows 7 pro, Powershell 4, and the destination machine is Windows 2012 R2 and also PowerShell 4.

Thanks in advance.