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The designer must create an instance of type 'Microsoft.Office.Tools.Ribbon.RibbonBase' but it cannot because the type is declared as abstract.

Hollister Everson 0 Reputation points
2026-01-27T21:12:56+00:00

No sure what happen to create this Issus, but I can no longer build by VSTO for Visio do to the ribbon will not open in Design. When I try to open the ribbon I get.

The designer must create an instance of type 'Microsoft.Office.Tools.Ribbon.RibbonBase' but it cannot because the type is declared as abstract.

and Instances of this error (1) 


 

1.   Hide Call Stack 

 

at Microsoft.DotNet.DesignTools.Serialization.CodeDomSerializerBase.Error(IDesignerSerializationManager manager, String exceptionText, String helpLink)

at Microsoft.DotNet.DesignTools.Serialization.TypeCodeDomSerializer.Deserialize(IDesignerSerializationManager manager, CodeTypeDeclaration declaration)

at Microsoft.DotNet.DesignTools.Sessions.Session.DeserializeToRootComponent(CodeTypeDeclaration typeDeclaration, String rootComponentClassName)

at Microsoft.DotNet.DesignTools.Sessions.Session.DeserializeRootComponent(CodeTypeDeclaration typeDeclaration, String rootComponentClassName, ResourceContentData[] resourceDocDataContent, String basePath)

at Microsoft.DotNet.DesignTools.Protocol.Endpoints.Sessions.InitializeRootComponentHandler.HandleRequest(InitializeRootComponentRequest request)

at Microsoft.DotNet.DesignTools.Protocol.Endpoints.RequestHandler`2.Microsoft.DotNet.DesignTools.Protocol.Endpoints.IRequestHandler.HandleRequest(Request request)
Microsoft 365 and Office | Visio | Other | Other

2 answers

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  1. Anonymous
    2026-01-28T05:47:35.63+00:00

    Dear @Hollister Everson,

    Welcome to Microsoft Q&A Forum!

    Based on the error you shared:

    “The designer must create an instance of type 'Microsoft.Office.Tools.Ribbon.RibbonBase' but cannot because the type is declared abstract…”

    This may typically happen when Visual Studio cannot reconstruct the Ribbon Designer class because something inside the project has changed in a way that breaks the designer’s ability to instantiate the Ribbon.

    Therefore, I have several suggestions that you can try to see if they can help you:

    1.Verify the Ribbon class definition:

    Please kindly check Ribbon1.cs:

    • Must be partial
    • Must not define its own constructor
    • Must not change base class
    • Namespace must match the .Designer.cs file

    Example of correct class:

    public partial class Ribbon1 : RibbonBase
{
    public Ribbon1()
        : base(Globals.Factory.GetRibbonFactory())
    {
        InitializeComponent();
    }
}

    2.Check references:

    You should open References and confirm:

    • Microsoft.Office.Tools.Common
    • Microsoft.Office.Tools.Ribbon
    • Office interop assemblies

    All must match:

    • The version of Office installed
    • The bit (32‑bit vs 64‑bit)

    If mismatched > the designer fails.

    3.Clean corrupted caches:

    You may try:

    • Close Visual Studio
    • Delete:
      • bin/
      • obj/
      • .vs/ (solution cache)
    • Reopen and rebuild

    This may resolve designer instantiation failures.

    4.If files were merged or edited manually:

    I recommend you can try this:

    • Compare .Designer.cs with a working version
    • Regenerate a fresh Ribbon (Designer) and manually copy his callbacks into it

    This may be the safest method to fix it.

    5.Create a fresh test project:

    Can you create a new Visio VSTO Add‑in with a new Ribbon (Designer), does it open normally?

    • If yes > the issue may be inside your project (file corruption or class mismatches).
    • If no > installation or reference version may mismatch on your machine.

    I hope this information can give you some insights and please feel free to update to me in comment section. Wish you a pleasant day!

    Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread. 

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  2. AI answer

    2026-01-27T21:13:07.3633333+00:00

    The error message you are encountering indicates that the designer is trying to create an instance of the RibbonBase class, which is abstract and cannot be instantiated directly. This typically occurs when there is an issue with the way the Ribbon is defined in your VSTO project for Visio.

    To resolve this issue, consider the following steps:

    1. Check Ribbon Class Definition: Ensure that your Ribbon class correctly inherits from RibbonBase and is not declared as abstract itself. You should have a concrete implementation of the Ribbon class.
    2. Rebuild the Project: Sometimes, simply cleaning and rebuilding the project can resolve design-time errors. In Visual Studio, right-click on the solution or project in Solution Explorer, select Clean, and then Rebuild.
    3. Check for Updates: Ensure that you are using the latest version of Visual Studio and the Office Developer Tools, as updates may contain fixes for known issues.
    4. Review Designer Support: Make sure that your version of Visual Studio supports the features you are trying to use in the Ribbon designer. If the designer you are using is not compatible, you may need to switch to a different one.
    5. Examine the Call Stack: The call stack provided in the error message may give you more context about where the issue is occurring. Look for any specific lines in your code that might be causing the problem.
    6. Consult Documentation: Refer to the official Microsoft documentation for guidance on using the Ribbon designer and troubleshooting issues related to it.

    If the problem persists after trying these steps, you may want to consider creating a new Ribbon item and migrating your existing code to it, as this can sometimes resolve underlying issues with the designer.

    AI-generated content may be incorrect. Read our transparency notes for more information.

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