Hi Martin,
I tried to reproduce the problem you describe but to no avail. I tested the following configurations:
1) A RadSlidingZone with ClickToOpen=true - when I click on the pane tab, the RadSlidingPane expands as expected.
2) I expand the RadSlidingPane on the server in the Click handler of a button using the ExpandedPaneId property of the RadSlidingZone.
3) I set the ExpandedPaneId property of the RadSlidingZone in the declaration of the control.
In all three cases, the RadSlidingPane opened as expected. I have attached my test page for your reference as well.
Could you please send me your RadSplitter definition and detailed information on the steps I need to follow in order to reproduce the problem?
I got it resolved as per the following link http://forums.asp.net/p/1066968/1546323.aspx
We had a problem with our frameborder being set to "yes" instead of "1" on the iframe.
Funny though it worked with the previous version of the toolkit:)
Thank you for your help.