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You may receive an error message when you try to close a Microsoft Windows Forms-based application. Consider the following scenario:
A Microsoft Windows Forms-based application uses ToolTips.
The application is running on the Microsoft .NET Framework 2.0.
In this scenario, you may receive the following error message when you try to close the application:
System.NullReferenceException: Object reference not set to an instance of an object.
A supported hotfix is now available from Microsoft, but it is only intended to correct the problem that is described in this article. Only apply it to systems that are experiencing this specific problem. This hotfix may receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next Microsoft .NET Framework 2.0 service pack that contains this hotfix.
To resolve this problem immediately, contact Microsoft Product Support Services to obtain the hotfix. For a complete list of Microsoft Product Support Services telephone numbers and information about support costs, visit the following Microsoft Web site:
Note In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The usual support costs will apply to additional support questions and issues that do not qualify for the specific update in question.
You must have the Microsoft .NET Framework 2.0 installed to apply this hotfix.
You do not have to restart the computer after you apply this hotfix.
Hotfix replacement information
This hotfix does not replace any other hotfixes.
The English version of this hotfix has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in Coordinated Universal Time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time item in Control Panel.
To work around this problem, include the following code as part of the Dispose method in every form that uses ToolTips.
If (Not Me.ToolTip1 Is Nothing) ThenMe.ToolTip1.RemoveAll()End IfMe.ToolTip1 = NothingEnd If
For example, to work around this problem, follow these steps:
Locate the following code in the Dispose method.
Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)If disposing ThenIf Not (components Is Nothing) Thencomponents.Dispose()End IfEnd IfMyBase.Dispose(disposing)End Sub
Replace the code that you located in step 1 with code that resembles the following code.
Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)If disposing ThenIf Not (components Is Nothing) Thencomponents.Dispose()End If----- Workaround code -----If (Not Me.ToolTip1 Is Nothing) ThenMe.ToolTip1.RemoveAll()End IfMe.ToolTip1 = Nothing----- Workaround code -----End IfMyBase.Dispose(disposing)End Sub
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:
824684 Description of the standard terminology that is used to describe Microsoft software updates