Looks like there is a bug in the Demo Viewer. When I go there, I get an ASP.NET exception.
https://demos.aspose.com/
Specifically, the problem is with the Document Builder demo.
I have checked the link you have provided and it seems to produce the demo document correctly. What browser are you using?
I was informed that there was a temporary problem on the website. Now it is fixed. Please check from your side if it is ok now.