Under VB6 you can generate graphic shapes – lines, circles, etc. – in a form’s Activate event handler. When this form is converted to VB.NET, you may observe that the graphic output is cleared immediately after the form becomes visible. This problem occurs only if the form’s AutoRedraw property is set to False.
The reason for this behavior is that .NET forms may receive an additional WM_ERASEBKGROUND message after the form becomes visible. This spurious message causes the form’s background to be cleared.
We recommend that you produce graphic output in the handler of the Paint event, rather than in the Activate event’s handler. If this remedy can’t be applied, you can fix the problem by setting the AutoRedraw property to True.