A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
You have to use Chart_Activate(), even if it is on its own sheet (which is not a "worksheet" even though it adds another sheet tab).
I got confused by this:
http://msdn.microsoft.com/en-us/library/office/ff198220%28v=office.15%29.aspx
...and the statement that it "Occurs when a workbook, worksheet, chart sheet, or embedded chart is activated.." (emphasis added)
The above references Worksheet.Activate (DOT and not an UNDERSCORE) and am not sure what the difference is (aside from it is for Office 2010 or 2013, but VBA scripts are the same in 2011 - maybe it's VB vs. VBA or such?), but so be it...
Sorry for the distraction!