Actually I didn't use the proper browser. With Firefox the constraints for Numeric text box and the DateInput of RadDatePicker are working fine(Numeric box not allowing letters and Date box formating typed numbers as date) except:
The RadDatePicker still not working... The date input is working fine, but when I click on the Pop Up button nothing happens. It doesn't matter if i add the DatePicker from code-behind or from the design view. Do you still think it's not properly configured AJAX?