“DTD is prohibited in this XML document” error

Users encountering an error during VisualSP installation at the Validating Information screen may experience a setback in the process. This error disrupts the validation of essential information, potentially preventing successful completion. The specific error message varies, providing clues about the nature of the problem. Addressing this issue is crucial, as the Validating Information step ensures accurate and compatible data for system integration.

Issue: The Subscription Admin sees the following error when they try to install VisualSP using the Installation Wizard:

Cause: The most common reason for this error is because the user's ISP is trying to be helpful and is sending the user to a friendly DNS failure page instead of letting it just fail when the DNS entry is not valid. Microsoft uses some DNS entries during the login process that are not actually valid entries and a proper failure response is required, but when the ISP intercepts that and provides a helper page it causes it to fail. There are several things you can try as a workaround:

1. Is the user logged into your network via VPN?
2. Try switching your DNS entry to use something else, like Google's (8.8.8).
3. Try disabling IPv6.
4. Add an entry to your hosts file.

Here is an article with a further description of the problem and things to try: https://www.koskila.net/fixing-security-reasons-dtd-prohibited-xml-document-issue/