menu rendering mode incompatibility

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C#

ASP.NET

I am using visual studio version 3.5 ... In order to use separator for database driven menu, I am using RenderingMode="Table". On using RenderingMode= table, separator was shown between menu item in design view but i got an error -

Error   17  'System.Web.UI.WebControls.Menu' does not contain a definition for 'RenderingMode' and no extension method 'RenderingMode' accepting a first argument of type 'System.Web.UI.WebControls.Menu' could be found (are you missing a using directive or an assembly reference?) 
and 
Error	18	The type or namespace name 'MenuRenderingMode' does not exist in the namespace 'System.Web.UI.WebControls' (are you missing an assembly reference?.

I had checked system.web properties and the version was 2.0.0.0.. Any help to solve this problem??.