Issue while editing appsettings.config file key and set the new value

Below is the code I am using and the error I am getting. Please advise and help.

Likewise I need to edit 2 more keys for timeout increase , please help on those ways of doing.

Code:

$ConfigFile = '<C:\Program Files\Apppath\bin\appSettings.config>'
## XML Node names and Attributes are CaSe SeNsItIvE!
$XPath = "root/config/add[@key='Command.DefaultTimeoutInSeconds']"
$Attribute = "30"
$NewValue = "180"

$xml = [xml](Get-Content -Path $ConfigFile)
$xml.SelectSingleNode($XPath).SetAttribute($Attribute,
$NewValue)
$xml.Save($ConfigFile)

Best Regards,SQLBoy