Hi Abdul Kadar,
I already answered your other thread and for your convenience and for others who might encounter the same issue I pasted my reply below:
Another possible reason for the problem could be if you have two RadWindowManager controls on your page (e.g if you have one manager on a MasterPage and another one on the content page or in a user control). Please, verify this and remove one of them and use the other one instead.
In case my assumptions and explanations do not help, please provide a fully runnable sample code along with detailed explanations of the exact desired behavior and I will do my best to help.
the Telerik team