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.
Answer:
This error can occur when MigrationWiz attempts to connect to OneDrive for Business, and the DNS record for msoid.<yourdomain> is resolving to something other than a CNAME pointing to clientconfig.microsoftonline-p.net.
Update your DNS record for msoid.<yourdomain> and confirm it to be a CNAME pointing to clientconfig.microsoftonline-p.net.
Please also review the following articles External Domain Name System records for Office 365 and What’s the purpose of the Office 365 CNAME record for MSOID?.