A new feature implemented in ASP.NET 4.0 is the possibility to control the way that controls’ ClientID is generated. At present, RadControls for ASP.NET AJAX expect the ClientID’s of their child controls to be generated by the default method (AutoID). Because of that, if ClientIDMode is set to different method of generation you can experience various problems with RadControls, for example not working dialogs for RadEditor.
Here are some of the errors that you could experience when the ClientIDMode is set to Static:
All RadControls: Invalid JSON primitive:..
RadEditor's dialogs : Error: 'null' is null or not an object
RadEditor's dialogs : Sys.ArgumentNullException: Dialog Parameters for the FindAndReplace dialog do not exist Parameter name: dialogueName.
RadFileExplorer: might not display the files in the folder
RadGrid : calling get_masterTableView() returns null
"Microsoft JScript runtime error: 'get_postBackElement().id' is null or not an object"
This problem is already added to our TODO list and it should be fixed for RadControls for ASP.NET AJAX Q2 2010. For the time being, we recommend to use ClientIDMode="AutoID" or if you have to use different method you should set the ClientIDMode property’s value explicitly to AutoID to the specific RadControl.
Additional information regarding this new .NET4.0 feature is available in the following article:
ASP.NET 4.0 ClientID Overview
Please note that Microsoft does not recommend setting ClientIDMode="Static" on pages which do contain dynamic controls.
The Telerik team