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.
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?.