Can you please verify that you are using the latest version 2009.3.1314 of RadControls for ASP.NET AJAX in your project and reference the respective GridFooterItem cell by replacing the "AggregatedColumnName" part with the actual UniqueName
value of the column?
Further information about how to access cells and rows in RadGrid for ASP.NET AJAX you can gather from the resources below:
the Telerik team
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