I am not sure what exactly you are doing your project and what is the exact problem. However, in case you are setting IDs of target controls, you should pass the ID of the target which is different than the wrapper ID of the DatePicker.
In case you experience further problems, please prepare a sample reproduction demo, open a new support ticket and send it to us along with detailed explanations of the actual and the desired behavior and reproduction steps. Once we have a better understanding on the exact setup, configuration and scenario, we will do our best to help.
the Telerik team