You're trying to use the Add
method of the Items collection with a string parameter. The Items
collection is a collection of objects of type RadItem,
in your case - objects of type RadListBoxItem
. You should always use objects of type RadListBoxItem
or its descendants when you work with Items collection.
Your code should be as follows:Dim test1 as RadListBoxItem = New RadListBoxItem("test11")
the Telerik team