Invalid Argument When Trying To Set File Permissions In Powershell - windows

Question

So I'm running a script that creates folders from a list of usernames in a CSV and in those folders it creates a folder called "Documents" and I'm then trying to give "modify" access rights to the "Documents" folder for the user concerned - eg a folder is created for john.smith, inside that folder is a "Documents" folder, and the user john.smith gets modify access rights to that "Documents" folder.
Creating the folders works without a hitch, it's the access rights part that is giving me a headache - it returns an Invalid Argument error for the last line of the code below and I can't figure out why - any help would be appreciated.
$Location = "C:\Scripts"
Set-Location $Location
$Folders = Import-Csv "C:\Scripts\UserFolderList.csv"
ForEach ($Folder in $Folders)
{
#Create A Folder From The "Name" Column In The CSV Then Create A Subfolder Called Documents
New-Item $Folder.Name -ItemType Directory
$Docs = "Documents"
$DocsPath = Join-Path $Folder.Name $Docs
New-Item -Path $DocsPath -ItemType Directory
#Assign The Modify Permission For The Username To The Documents Folder
$Domain = "tly"
$DomainUser = $Domain + $Folder.Name
$FullDocsPath = "$Location" + $Folder.Name + "$Docs"
$Acl = Get-Acl $FullDocsPath
$ArgumentList="$DomainUser","Modify","ContainerInherit,ObjectInherit","None","Allow"
$AccessRule = New-Object System.Security.AccessControl.FileSystemAccessRule ($ArgumentList)
$Acl.SetAccessRule($AccessRule)
Set-Acl -path $FullDocsPath -aclObject $AccessRule
}
The resulting error is:
Set-Acl : AclObject
At line:22 char:1
Set-Acl -path $FullDocsPath -aclObject $AccessRule
CategoryInfo : InvalidArgument: (System.Security...ystemAccessRule:FileSystemAccessRule) [Set-Acl], ArgumentException
FullyQualifiedErrorId : SetAcl_AclObject,Microsoft.PowerShell.Commands.SetAclCommand