I suppose that by "docked", you mean "expanded", as when a RadSlidingPane is docked, it has "position:static".
As when a RadSlidingPane is expanded, it has "position:absolute;z-index:2000", you simply need to apply a greater z-index than 2000 to the Menu control. In order for this setting to take effect, you have to apply a position to the Menu as well. The easiest way to get the menu to display over the RadSlidingPane in this case, is to wrap the Menu in the following DIV element:
|<div style="position: relative; z-index: 3000">
In case this does not help, please prepare and send us a simple working project, demonstrating the problem, so that we can research what is causing it.
the Telerik team
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