.NET Questions and Solutions

Symptoms
If you use the CommandBuilder object to explicitly get commands for the DataAdapter object as follows:

da.InsertCommand = cb.GetInsertCommand and then run the following Visual Basic .NET code

cb.DataAdapter = Nothing or the following Visual C# .NET code

cb.DataAdapter = null; the commands that you add to the DataAdapter are deleted, and you receive the following error message:

An unhandled exception of type ‘System.NullReferenceException’ occurred in app_name.exe
Additional information: Object reference not set to an instance of an object.
Resolution
CommandBuilder deletes the commands that it generates when it is disassociated from a DataAdapter. CommandBuilder and DataAdapter are linked; when they are unlinked or disassociated, the commands are nulled. This problem does not affect commands that you build from the beginning (from scratch).

Symptoms
In a Microsoft Visual Basic 2005 or Microsoft Visual Basic .NET application, when you pass late-bound parameters to methods of Microsoft Office objects, you may receive COMException exceptions. For example, when you pass the Name property of a late-bound UserProperty object to the UserProperties.Items method, you may receive the following error message:

An unhandled exception of type ‘System.Runtime.InteropServices.COMException’ occurred in microsoft.visualbasic.dll
Additional information: Property is read-only.Note Similar symptoms may also occur when you call methods of other Microsoft Office objects.
Resolution
If you pass a property of an object to a method by reference and the property has a set accessor, Visual Basic calls the set accessor to set the property to the value that the method returns. At compile time, if you pass a property of a late-bound object, the Visual Basic compiler cannot determine whether the property is passed by reference. Also, the Visual Basic compiler cannot determine whether the property has a set accessor. Therefore, the Visual Basic compiler permits the late binder to determine these details at run time.
However, if the relevant objects are Component Object Model (COM) objects at run time, the late binder cannot obtain sufficient information about these details. The late binder uses managed reflection to try to determine these details. The late binder assumes that such method calls involve a ByRef parameter and that the property that you pass has a set accessor. If the property that you pass does not have a set accessor, the Microsoft .NET Framework generates a MissingMethodException exception. The late binder handles the MissingMethodException exception.
The .NET Framework generates a MissingMethodException exception when the call to a method of a Microsoft Office object returns a HRESULT value of COR_E_MISSINGMETHOD. The Microsoft Office object is a COM object. Visual Basic .NET incorrectly assumes that all the methods of Microsoft Office objects return COR_E_MISSINGMETHOD if the property that you pass does not have a set accessor. However, not all the methods of Microsoft Office objects return COR_E_MISSINGMETHOD if the property that you pass does not have a set accessor. Therefore, the behavior that is mentioned in the “Symptoms” section of this article occurs if you pass a property that does not have a set accessor, such as the UserProperty.Name property, to a method.
Note This behavior does not occur if you use early-bound Microsoft Office objects.

Symptoms
In Microsoft Visual Studio 2005 or in Microsoft Visual Studio .NET, when you set the ImageList property of the CoolBar ActiveX control to the ImageList ActiveX control, and then you run the application, you receive the following exception:

An unhandled exception of type ‘System.Runtime.InteropServices.COMException’ occurred in axinterop.comctl3.dll
Additional information: Invalid property value. Note You cannot set the ImageList property of the CoolBar ActiveX control in the Properties window.
Resolution
Microsoft Visual Basic 2005, Microsoft Visual Basic .NET, and Microsoft Visual C# .NET interpret the ImageList property of the CoolBar ActiveX control as a read-only property. Therefore, Visual Basic 2005, Visual Basic .NET, and Visual C# .NET throw an exception when you set the ImageList property of the CoolBar ActiveX control to the ImageList ActiveX control.

Symptoms
You run a Visual Basic application that uses the CreateObject function tostart a hidden instance of Microsoft Word. The application is idle, but itstill maintains a reference to Word. Next, you manually start an instanceof Word. A separate instance of Word should open, but the same instancethat was created by the Visual Basic application is made active instead. Ifyou close Word and continue to work in the Visual Basic application, one of the following errors occurs when the application tries to use Word objectsbecause Word is no longer running:

Run-time error ‘462′:
The remote server machine does not exist or is unavailable
-or-

Run-time error ‘-2147023174 (800706ba)’:
Automation errorThis automation error translates to “The RPC server is unavailable.”
Resolution
Use one of the following to work around this problem:Before you create your Word object, first create a temporary Wordobject. After you create your object, close the temporary object. Thiscauses Word to act properly when you control it through Automation (thatis, if a user interactively starts Word, a new instance of Word isopened for the user). The automation instance remains hidden andseparate. See the Steps to Reproduce Behavior section for an example ofthis workaround.Make the Word object visible immediately after using the CreateObjectfunction. This workaround is only for Microsoft Word 97. For example:

Set wrdApp = CreateObject(“Word.Application”)wrdApp.Visible = True

Symptoms
In Visual Basic 6.0, removing elements from the end of a collection takeslonger than removing elements from the beginning.
Resolution
When removing an element from a collection, Visual Basic 6.0 begins at thebeginning of the collection and traverses the collection until the desiredelement is reached, then that element is removed.

Symptoms
When you try to pass a Collection object fromMicrosoft Visual Basic 6.0 components to Microsoft Visual Basic 2005 or to Microsoft Visual Basic .NET, you may receive an error message. In Microsoft Visual Studio 2005, you receive the following error message:

An unhandled exception of type ‘System.InvalidCastException’ occurred in ApplicationName.exe
Additional information: Unable to cast object of type ‘Microsoft.VisualBasic.Collection’ to type ‘VBA.Collection’.In Microsoft Visual Studio .NET, you receive the following error message:

An unhandled exception of type ‘System.InvalidCastException’ occurred in ApplicationName.exe
Additional information: Specified cast is not valid.If you examine the type of the collection object that Visual Basic 2005 or Visual Basic .NET expects, you find that Visual Basic 2005 or Visual Basic .NET expects the VBA.Collection type instead of the Microsoft.VisualBasic.Collection type. If you change your code to pass a collection object of the VBA.Collection type, you receive the following error message on the line of code where you try to create a new instance of the VBA.Collection class:

An unhandled exception of type ‘System.Runtime.InteropServices.COMException’ occurred in ApplicationName.exe
Additional information: COM object with CLSID {A4C4671C-499F-101B-BB78-00AA00383CBB} is either not valid or not registered.This problem also occurs in other Microsoft .NET Framework-supported languages such as Microsoft Visual C# 2005 and earlier versions of .NET Framework-supported Microsoft Visual C#.
Resolution
The InvalidCastException error occurs because the Microsoft.VisualBasic.Collection type is incompatible with the VBA.Collection type. The COMException error occurs because only a Visual Basic 6.0 application can create an instance of the VBA.Collection class. You cannot create an instance of the VBA.Collection class outside a Visual Basic 6.0 application.