Hello Princy, thanks for your answer.
This works fine when i use it at the page load event but I have stille a problem when I use it with a radgrid and the itemcommand object.
See the code below. Where is my mistake? The pageview change correctly to the new index but not the Tab to the Child Tab.
protected void Grid1_ItemCommand(object source, GridCommandEventArgs e)
GridDataItem dataItem = e.Item as GridDataItem;
string AbrechnungsID= dataItem["Test_ID"].Text;
rtsTab.Tabs.SelectedIndex = 1;
RadPageView.SelectedIndex = 5;