John, thank you for all, but it doesn't work again.
Now, the row9 is OK, but the same error is appeared on row12
Voltage = Application.WorksheetFunction.Average(Range("B1:B" & i))

VBA select the word "Range(...)" and said the above message.
I have tryed to put "ActiveSheet" before "Average"(or before "WorksheetFunction, or before "Application") but it doesn't work.