Network issue when connecting to SharePoint Online.
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.
The problem seems to be a well know issue with some Internet providers (your local internet connection).
There are many many links about it: Its essentially a DNS problem on the ISP side (maybe 2 routers) on your network.
(scroll down and have a look at the comments)
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