unable to populate receive connector

i have more than 100 ip addresses to be added in the scope of my receive connector. i'm trying to use powershell

$ReceiveConnector = Get-ReceiveConnector "Allow Relay External Emails"
Get-Content d:\list2.txt | foreach {$ReceiveConnector.RemoteIPRanges += "$_"}
Set-ReceiveConnector $ReceiveConnector -RemoteIPRanges $ReceiveConnector.RemoteIPRanges

i have a text file "list2.txt" that contains the ip addresses. one ip address per line. whenever i ran the above code, i get below error message:

The operation couldn't be performed because object 'mb2.ACME.com\Allow Relay External Emails'
couldn't be found on 'dc02.ACME.COM'.