cannot iterate random numbers 1000 times

Now that I (finally) understand your question, I don't know the answer.

But maybe this will save your finger some wear and tear:

Sub x()
    Dim i       As Long

    With Application
        .Iteration = True
        .MaxIterations = 1
    End With

    Range("A1:A10").Formula = "=randbetween(0,1)"
    Range("A12").Formula = "=--(sum(a1:a10) >= 6)"
    Range("A13").Formula = "=a12 + a13"

    For i = 1 To 1000
        Range("A13").Calculate
    Next i
End Sub