Hi Stanley Huang,
You can either use the RadControls installer that installs the Telerik.Charting assembly in the GAC, or you can install the dll manually via the gacutil tool (you can find help article how to do that here
Alternatively, if you cannot or do not wish to install the Telerik.Charting assembly in the GAC on your server, you can reference the dll as a private assembly (from the project /bin folder instead from the GAC) but note that in this case you need to modify all references to the Telerik.Charting assembly (ASPX files, web.config) to reference the local assembly, and not the GAC.
the Telerik team
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