In this case, I can recommend the following:
- We will release a SP next week, please update your version to that SP. We have made some changes to VisibleDuringInit functionality of the RadSplitter and now it loads faster when you have VisibleDuringInit=false and a lot of content in the RadPanes. In case you need it earlier, you can download our latest internal build from http://www.telerik.com/account/latest-internal-builds.aspx.
- You can ajaxify the navigation control in your left RadPane to update only the RadGrid in the right RadPane - you can use RadAjaxManager (http://demos.telerik.com/aspnet-ajax/Ajax/Examples/Manager/FirstLook/DefaultCS.aspx) for this purpose.
the Telerik team
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