Goal seek

Hello,

I'm new to VBA so this may be a trivial question.

I'm trying to run goalseek down a single column by changing the cell from another column in a different sheet.

My code is as follows:

Sub MinDiffExit()
    Dim i As Integer
    i = 1
    For i = 1 To 64
    Cells(i + 3, 16).GoalSeek Goal:=0, ChangingCell:=Sheets("Yields").Cells(i + 20, 6)
    Next i
End Sub

The code works but I get a run time error? Why is this and how can I fix it?

Any help would be much appreciated.