For XMP-2200 series and XDS-1060 series, please update to Manager Express 4.3.40 or later to resolve this issue.
For all other models, here's why certain web sites won't work:
Manager Express uses iframe technology to implement Webpage widget.
Some web sites such as YouTube and Google do not allow user to display their web page through iframe.
That is why these sites could not be displayed through Webpage widget.
Ref : http://en.wikipedia.org/wiki/HTML_element#Frames