AccessViolationException was unhandled? - vb.net

Question

I'm working on a directory Project where in when the program is not being use or idle for 3 minutes, a form that act as stand-by screen that plays a video will show (I use AxWindowsMediaPlayer). By clicking anywhere in the form, the stand-by screen will close and will be back to the main form.
The program works fine but SOMETIMES during the closing of stand-by screen form, the application crashes with the error:
AccessViolationException was unhandled. Attempted to read or write
protected memory. This is often an indication that other memory is
corrupt.
and this is the complete error detail:
System.AccessViolationException was unhandled
Message=Attempted to read or write protected memory. This is often an indication that other memory is corrupt.
Source=System.Windows.Forms
StackTrace:
at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
at System.Windows.Forms.Application.RunDialog(Form form)
at System.Windows.Forms.Form.ShowDialog(IWin32Window owner)
at System.Windows.Forms.Form.ShowDialog()
at BuildingDirectory.main.tmrTime_Tick(Object sender, EventArgs e) in C:\Users\pc\Documents\Visual Studio 2010\Projects\testing\BuildingDirectory\BuildingDirectory\main.vb:line 128
at System.Windows.Forms.Timer.OnTick(EventArgs e)
at System.Windows.Forms.Timer.TimerNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
at System.Windows.Forms.Application.Run(ApplicationContext context)
at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.OnRun()
at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.DoApplicationModel()
at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.Run(String[] commandLine)
at BuildingDirectory.My.MyApplication.Main(String[] Args) in 17d14f5c-a337-4978-8281-53493378c1071.vb:line 81
at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ThreadHelper.ThreadStart()
InnerException:
The weird thing is, the line of code where the error is pointing, is enclosed in try catch block specifically catching AccessViolationException(it was exception before but still encountered the problem):
Private Sub tmrTime_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles tmrTime.Tick
Try
lblTime.Text = TimeOfDay
If standby = 2 Then
standby += 1
standByScreen.ShowDialog() ---> this is where the error is pointing to
Else
standby += 1
End If
Catch ex As AccessViolationException
MessageBox.Show(ex.ToString)
End Try
End Sub
Please help me, thank you

Answer 1

This might be due to early binding of the standByScreen variable. Note that the error is caused due to the System.Windows.Forms class
Try:
Dim stndByScreen As Object
stndByScreen = standByScreen
stndByScreen.ShowDialog()
instead of directly using standByScreen