求助：刚学VFP，最近做练习时遇到一闪退出的问题

最近刚刚学习VFP，用VFP6.0做了一个叫倒计时程序的练习。运行后闪了一下就退出程序了，想问一下应该怎么办呢？谢谢了。代码如下：

If This.Caption="开始（＆B）"
   This.Caption="停止（＆S）"
   ThisForm.Timer1.Enabled=.T.
   ThisForm.SpinHour.ReadOnly=.T.
   ThisForm.SpinMin.ReadOnly=.T.
   ThisForm.SpinSec.ReadOnly=.T.
Else
   This.Caption="开始（＆B）"
   ThisForm.Timer1.Enabled=.F.
   ThisForm.SpinHour.ReadOnly=.F.
   ThisForm.SpinMin.ReadOnly=.F.
   ThisForm.SpinSec.ReadOnly=.F.
EndIf   

If(ThisForm.SpinHour.Value=0).And.(ThisForm.SpinMin.Value=0).And.(ThisForm.SpinSec.Value <= 1)
ThisForm.SpinSec.Value=0
ThisForm.Command1.Caption="开始(＆B)"
This.Enabled=.F.
ThisForm.SpinHour.ReadOnly=.F.
ThisForm.SpinMin.ReadOnly=.F.
ThisForm.SpinSec.ReadOnly=.F.
Else
If ThisForm.SpinSec.Value=0
   ThisForm.SpinSec.Vaule=59
   If ThisForm.SpinMin.Value=0
     ThisForm.SpinMin.Value=59
     ThisForm.SpinHour.Value=ThisForm.SpinHour.Value-1
   Else
     ThisForm.SpinMin.Value=ThisForm.SpinMin.Value-1
   EndIf  
Else
     ThisForm.SpinSec.Value=ThisFomr.SpinSec.Value-1
   EndIf
EndIf

要在适当的事件或过程中使用read event命令。