while Schleife abbrechen geht nicht

Private Sub Form_KeyDown(KeyCode As Integer, Shift As Integer)
If KeyCode = 27 Then b = False
End Sub

Private Sub start_program()
On Error GoTo ErrorHandler
Dim idn As String
Dim i As Integer
Dim ic As Integer
Dim c As Integer
Dim Z As Integer
Dim tst As String
Dim volt As Double
Dim curr As Double
Dim INP As Double
Dim Vstepa As Double
Dim Tstepa As Double
Dim NoVal As Double
Dim slist As String
Dim voca As Double
Dim numdat As String
Dim Sh1 As Worksheet
Set Sh1 = ActiveSheet
INP = 1
voca = tbLoadBank11.Value     ' Startwert Spannung
Vstepa = tbLoadBank13.Value   ' Step der Spannung
Tstepa = tbLoadBank14.Value   ' Zeit pro Step
NoVal = tbLoadBank15.Value    ' Messpunkte pro Step
b = True
i = 0
Z = 0
Sh1.Cells(1, 1) = "Timestamp"
For ic = 11 To 18
If UserForm1.Controls("ch" & ic).Value  "   " Then
Sh1.Cells(1, ic - 9) = UserForm1.Controls("name" & ic).Value + "  [" + UserForm1. _
Controls("label" & ic) + "]"
Else
Sh1.Cells(1, ic - 9) = ""
End If
Next
Do While (voca > 0 Or b = True)
DoEvents
i = i + 1
Z = Z + 1
Sh1.Cells(i + 1, 1) = Now()
Application.Wait (Now() + TimeValue(Format(Tstepa / 86400, "hh:mm:ss")))
For c = 1 To numdat
UserForm1.Controls("display" & c + 10).Value = Sh1.Cells(i + 1, c + 1)
Next
If Z = NoVal Then
voca = voca - Vstepa
Z = 0
End If
Loop
MsgBox "Stop loop!"
Exit Sub
ErrorHandler:
MsgBox ("Something went wrong! Start failed!")
End Sub