The Sage CRM Developer Program website has recently changed and the address dpp.sagecrm.com is being discontinued.
The equivilant link on the new website is https://community.sagecrm.com/blogs/hints_tips_and_tricks/archive/tags/Sage CRM 6.1/default.aspx
Alternatively continue to the Sage CRM home page or the Sage CRM Partner Community home page.