Item cannot be added to the Toolbox.
This error generally occurs when you attempt to add an item for which the Toolbox cannot display a shortcut icon.
Items which the Toolbox can display include:
Controls and .NET Framework components installed on your local machine.
Note Controls and components for ASP.NET Web forms must have an AspNetHostingPermission.Level Property of "Unlimited" to be displayed in the Toolbox.
Selected text dragged or pasted from a Visual Studio editor, such as code snippets.
Items which the Toolbox cannot display include:
Excel workbook files.
.NET Framework assemblies installed on shared network servers.
An assembly added from a UNC path is not fully trusted, so it is not granted sufficient permissions to be displayed in the Toolbox.
To correct this error
Use the Customize Toolbox dialog box to add a control or component that is installed on your local machine to the active Toolbox tab.
- or -
Drag or paste selected text from a Visual Studio editor onto the Toolbox.