I am getting an error while running a powershell script targeting SharePoint online Site.
For security reasons DTD is prohibited in this XML document. To enable DTD processing set the DtdProcessing property on XmlReaderSettings to Parse and pass the settings into XmlReader.Create method
Have you already tried what the error text says?
XmlReaderSettings settings = new XmlReaderSettings();
settings.DtdProcessing = DtdProcessing.Parse;
Then pass settings as the second argument to XmlReader.Create
https://msdn.microsoft.com/en-us/library/system.xml.xmlreadersettings.dtdprocessing(v=vs.110).aspx
