The Sage CRM Developer Program website has recently changed and the address dpp.sagecrm.com is being discontinued.
The equivalent link on the new website is https://community.sagecrm.com/blogs/talking_about_customers/archive/tags/http_3A002F002F00_www.dofonline.co.uk/default.aspx
Alternatively continue to the Sage CRM home page or the Sage CRM Partner Community home page.