ChartObject for Worksheet object in Excel

Hi!

I try to get ChartObect from Worksheet writing the following

Code:

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ActiveSheet.ChartObjects("Diagram 1").Activate

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but I get error

Run-time error '1004'
Impossible to retreive ChartObject of Worksheet class


What I have to do to make available this property of Workshet? May be I must turn on some reference?

With best regards,
Yura.