Caution ADO and ADO MD have not been fully tested in a Microsoft .NET Framework environment. They may cause intermittent issues, especially in service-based applications or in multithreaded applications. The techniques that are discussed in this article should only be used as a temporary measure during migration to ADO.NET. You should only use these techniques after you have conducted complete testing to make sure that there are no compatibility issues. Any issues that are caused by using ADO or ADO MD in this manner are unsupported. For more information, see the following article in the Microsoft Knowledge Base:
840667 You receive unexpected errors when using ADO and ADO MD in a .NET Framework application
You deploy a Microsoft .NET Framework application that accesses a database on a computer. The computer only has the .NET Framework Redistributable package installed. When you run the application, you may receive the following error message:
An unhandled exception has occurred in your application. If you click Continue, the application will ignore this error and attempt to continue. If you click Quit, the application will be shut down immediately. QueryInterface for interface ADODB._Command failed.
The problem occurs because Microsoft Data Access Components (MDAC) is not installed on the computer. The .NET application uses MDAC to access the data from the database.
To resolve this problem, install MDAC on the computer. You can download MDAC from the following Microsoft Developer Network (MSDN) Web site:
Microsoft ADO.NET 1.0, Microsoft ADO.NET 1.1, Microsoft ADO.NET 2.0, Microsoft ActiveX Data Objects 2.7, Microsoft Visual Basic .NET 2002 Standard Edition, Microsoft Visual Basic .NET 2003 Standard Edition, Microsoft Visual C# .NET 2002 Standard Edition, Microsoft Visual C# .NET 2003 Standard Edition