Removing the dashes from the Control ID fixed the problem for the Datepicker, thanks.
If there is a full postback caused by another control then it works.
I think the problem is because the RadWindow is a part of a user control that is added to the page dynamically and the script does not appear to be added to the page.
I have sent a zip folder with 3 user controls using My client.net.
These are as follows,
MediaSpaceCRUD.ascx - This is the main control with 2 buttons. These 2 buttons will dynamically add the other controls ImageItem.ascx and EventsNewsItem.ascx to the page. An ImageItem will be added to the page using ajax and when it is added clicking on the select link does nothing, but if add a EventsNewsItem to the page this will cause a full postback and then clicking on the select link will open the RadWindow.
There is an App_Code folder containing a DataContext class and an App_Data folder containg a sql script to create 2 tables which the controls use.