Option Explicit
 
Private CancelFlag As Boolean
Private RunnningFlag As Boolean, flgNeustart As Boolean
 
Private Sub Form_Load()
  flgNeustart = False
  CancelFlag = False
  RunnningFlag = False
End Sub
 
Private Sub Command1_Click()
' Starten
  Label1.Caption = ""
  If RunnningFlag = False Then
    Call StackTest
  Else
    flgNeustart = True
    CancelFlag = True
  End If
End Sub
 
Private Sub Command2_Click()
' Abbruch
  flgNeustart = False
  CancelFlag = True
End Sub
 
Private Sub StackTest()
 
  Dim i As Long
 
  RunnningFlag = True
  Do
    flgNeustart = False
    For i = 0 To 100000
      Label1.Caption = Str$(i)
      DoEvents
      If CancelFlag = True Then
        CancelFlag = False
        Exit For
      End If
    Next i
  Loop While flgNeustart = True
  RunnningFlag = False
End Sub

Gruss,

Zardoz