"Invalid directory on URL" while trying to use path created using New-PSDrive in Powershell

I have written a function to get authentication token. I have used New-PSDrive because PathTooLongException was thrown. Write-Host $adal, (Test-Path $adal) returns True while testing if path exists. But throws exception in LoadFrom(). Could someone help me get rid of the error?

Code:

function GetAuthToken {
    try{
        Write-Host "GetAuthToken-Start"
        If (!(Test-Path CustomDrive:)){
            $adalPath = Get-Module -Name "AzureRM.Profile" -ListAvailable -All | Select -First 1 | Select -ExpandProperty ModuleBase
            New-PSDrive -Name "CustomDrive" -PSProvider filesystem -Root $adalPath
            Write-Host "Created CustomDrive."
        }
        
        $adal = "CustomDrive:\Microsoft.IdentityModel.Clients.ActiveDirectory.dll"
        $adalforms = "CustomDrive:\Microsoft.IdentityModel.Clients.ActiveDirectory.WindowsForms.dll"
            
        Write-Host $adal, (Test-Path $adal) #Test-Path returns True
        Write-Host $adalforms, (Test-Path $adalforms)
        
        Write-Host "Loading required DLLs..."
        [System.Reflection.Assembly]::LoadFrom($adal) | Out-Null #This line throws exception
        [System.Reflection.Assembly]::LoadFrom($adalforms) | Out-Null
        Write-Host "Loaded required DLLs successfully."

        Write-Host "Trying to acquire token..."
        $authContext = New-Object "Microsoft.IdentityModel.Clients.ActiveDirectory.AuthenticationContext" -ArgumentList $authorityUri
        $authResult = $authContext.AcquireToken($resourceUri, $clientId, $redirectUri, "Always") 
        Write-Host "Acquired token successfully."

        Write-Host $authResult
        Write-Host "GetAuthToken-End"
        return $authResult
    }
    catch{
        Write-Error -Message $_.Exception
        throw $_.Exception
    }
    finally{
        Remove-PSDrive -Name "CustomDrive"
        Write-Host "Removed CustomDrive."
    }
}

Exception:

GetAuthToken : System.Management.Automation.MethodInvocationException: Exception calling "LoadFrom" with "1" argument(s): "Invalid directory on 
URL." ---> System.ArgumentException: Invalid directory on URL.
   at System.Security.Util.DirectoryString.CreateSeparatedString(String directory)
   at System.Security.Util.URLString.ParseFileURL(String url)
   at System.Security.Util.URLString.GetFileName()
   at System.Reflection.RuntimeAssembly.InternalLoadAssemblyName(AssemblyName assemblyRef, Evidence assemblySecurity, RuntimeAssembly 
reqAssembly, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean 
suppressSecurityChecks)
   at System.Reflection.RuntimeAssembly.InternalLoadFrom(String assemblyFile, Evidence securityEvidence, Byte[] hashValue, AssemblyHashAlgorithm 
hashAlgorithm, Boolean forIntrospection, Boolean suppressSecurityChecks, StackCrawlMark& stackMark)
   at System.Reflection.Assembly.LoadFrom(String assemblyFile)
   at CallSite.Target(Closure , CallSite , Type , Object )
   --- End of inner exception stack trace ---
   at System.Management.Automation.ExceptionHandlingOps.CheckActionPreference(FunctionContext funcContext, Exception exception)
   at System.Management.Automation.Interpreter.ActionCallInstruction`2.Run(InterpretedFrame frame)
   at System.Management.Automation.Interpreter.EnterTryCatchFinallyInstruction.Run(InterpretedFrame frame)
   at System.Management.Automation.Interpreter.EnterTryCatchFinallyInstruction.Run(InterpretedFrame frame)

Thanks to @mclayton for letting know the root cause.

Used Add-Type instead of LoadForm() to load the assembly in powershell.

Add-Type -Path $adal