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Editorial Team
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Asked: 2026-05-26T12:22:18+00:00

Why does my Visual Studio show the error: The type or namespace name ‘Compatibility’

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Why does my Visual Studio show the error:

The type or namespace name ‘Compatibility’ does not exist in the namespace ‘Microsoft.VisualBasic’ (are you missing an assembly reference?)

when I do have Microsoft.VisualBasic.Compatibility component already referenced under the .NET tab of Add Reference dialog box.

My .net knowledge is at very basic level. I did google the issue but couldn’t find relevant solutions. Any help, hint, suggestion, links will be much appreciated.

EDIT

The project is actually an Outlook 2003 add-in in C#.

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1 Answer

  1. Editorial Team

    You havn’t shown the code that results in the error. However, the Microsoft.VisualBasic.Compatibility assembly only contains a single namespace Microsoft.VisualBasic.Compatibility.VB6. My guess is that you need to include this statement in your code

    using Microsoft.VisualBasic.Compatibility.VB6;

    You state that you .NET knowledge is at a very basic level so let me try to clarify a bit.

    Adding a reference to an assembly in your project allows you to instantiate types defined in that assembly and execute code belonging to these types. Simplifying things a bit you can think of the assembly name as the name of the file with the code without the DLL extension. In this case the name of the assembly is Microsoft.VisualBasic.Compatibility.

    To avoid identificer collisions .NET has the concept of a namespace. Namespaces are hierarchical in nature just as internet domain names are. The Microsoft.VisualBasic.Compatibility.VB6 namespace is in the top-level Microsoft namespace with three subordinate namespaces.

    To refer to a type you need to qualify it by using the namespace, e.g the fully qualified name of the ScaleMode enumeration is Microsoft.VisualBasic.Compatibility.VB6.ScaleMode. However, you soon get tired of doing that and most of the time you will import all the types from a namespace by putting an using statement at the start of your source file as shown above. Then you can simply refer to the ScaleMode enumeration in your code.

    The confusing part here is that the assembly name is almost the same as the namespace you need.

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