Running ADUC as different user - wrong directory - powershell

Question

I'm fairly new to powershell.
In this code my coworkers are getting an error which I'm not getting.
I've tried some different things (like adding the complete path to powershell) but I'm not able to fix it.
Can anyone tell me what's going wrong?
Function Button4_Click()
{
$Filepathmmc = join-path -path $env:SystemRoot -ChildPath System32\Mmc.exe
$argumentlistdsa = join-path -path $env:SystemRoot -ChildPath System32\dsa.msc
$Credential = New-Object -TypeName System.Management.Automation.PsCredential -ArgumentList (Get-Content "$($env:userprofile)\username.txt"),(Get-Content "$($env:userprofile)\encrypt.txt" | ConvertTo-SecureString)
Start-Process powershell -Credential $Credential -ArgumentList "Start-Process -FilePath '$filepathmmc' -ArgumentList '$argumentlistdsa' -Verb RunAs"
}
I also tried using this as the Start-Process path:
$aducpath = (Join-Path $Env:SystemRoot -ChildPath "\syswow64\WindowsPowerShell\v1.0\powershell.exe")
Needs elevation

Answer 1

I see that you are still using join-path, have you tried using an absolute path for the sake of troubleshooting?
I also see that you're reading a password from a text file. I would advise you not to do that, and instead maybe have users log in themselves instead for elevation. If you replace $Credential in the invocation process with (Get-Credential) it will prompt your user for elevation. You can also use $Credential = Get-Credential to save it for the future.
I can't reproduce the error you're getting with just this code snippet. All of your Join-Paths are sane and seem to point to the expected place. When run as an unprivileged user, I get a UAC prompt rather than the invalid code. If there is actually a problem with where things are, might I suggest that you use something like this to search for what you need?
Function Button4_Click()
{
$Filepathmmc = (Get-ChildItem -Recurse -Path $env:SystemRoot -Filter "Mmc.exe").FullName | Select-Object -First 1
$argumentlistdsa = (Get-ChildItem -Recurse -Path $env:SystemRoot -Filter "dsa.mmc").FullName | Select-Object -First 1
Start-Process powershell -Credential (Get-Credential) -ArgumentList "Start-Process -FilePath '$filepathmmc' -ArgumentList '$argumentlistdsa' -Verb RunAs"
}
It's not perfect, but it will always return an instance of mmc. You can add -ErrorAction SilentlyContinue to the Get-ChildItem command to suppress the inevitable 'Accesss to the path X is denied' exceptions.