How to work with every cell in an array?

[Radka]

I have started to execute the Sub by F8 and on "8 row of the Sub" the message above is appeared. And this is happend with another Sub, which consists "Range(...)".
My last Sub is:

Sub Voltage() 
Dim Voltage
Dim Difference
Dim i As Integer
Dim AvrPoints As Boolean
AvrPoints = False
Dim LastRow As Long
LastRow = Range("B65536").End(xlUp).Row
Do Until AvrPoints = True
For i = 1 To LastRow
Voltage = Application.WorksheetFunction.Average(Range("B1:B" & i))
Diference = Cells(i + 1, 2) - Voltage
If Difference > 0.0004 Then
AvrPoints = True
End If
Next i
Loop
MsgBox Voltage
End Sub