Unfortunately you cannot attach archives to forum threads. I advise you to open a new support ticket with your project attached there.
Still I will try to help you as much as possible based on the description you have provided so far.
Please, find attached a sample page with a custom implementation of a RadTreeView with RadGrid inside a RadSplitter. The RadTreeView updates the RadGrid through Ajax requests. In the RadGrid the selecting of rows is enabled through ClientSettings-Selecting-AllowRowSelect="true"
. In the event handler for ClientSettings-ClientEvents-OnRowSelected
you should implement the logic to update the content of the data view pane.
As far as the Target="_blank" question is concerned - this is a property of a RadTreeView Node. Please, check the definitions of the nodes and see if there are any usages of Target. If there are, please, check the behavior of the RadTreeView if you remove them.
Hope I have been of help.
All the best,
the Telerik team