Hi Radu Nitu,
With the Q2 Release RadDataPager was moved to the new assembly called Telerik.Windows.Controls.Data.
Add a reference to this new assembly.
Here are the release notes
I hope this helps.
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items