PlugInId cannot be GUID.empty - Id property is a getter only?

When I load an add-in via Options > Plug-ins > Install I see the following error:

The Id property of the PlugIn class is read-only. Guid attributes have been added to the panel classes. How do I fix this issue?

EDIT: I’m using the CORE 7 project template with net48 as the target framework and the LangVersion property in csproj set to preview so I can benefit from the latest language features. Maybe this is the cause?

I believe you should check your AssemblyInfo file

Example :

using Rhino.PlugIns;
using System.Reflection;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;

// Plug-in Description Attributes - all of these are optional.
// These will show in Rhino's option dialog, in the tab Plug-ins.
[assembly: PlugInDescription(DescriptionType.Address, "")]
[assembly: PlugInDescription(DescriptionType.Country, "")]
[assembly: PlugInDescription(DescriptionType.Email, "")]
[assembly: PlugInDescription(DescriptionType.Phone, "")]
[assembly: PlugInDescription(DescriptionType.Fax, "")]
[assembly: PlugInDescription(DescriptionType.Organization, "Ship Designer")]
[assembly: PlugInDescription(DescriptionType.UpdateUrl, "")]
[assembly: PlugInDescription(DescriptionType.WebSite, "")]

// Icons should be Windows .ico files and contain 32-bit images in the following sizes: 16, 24, 32, 48, and 256.
[assembly: PlugInDescription(DescriptionType.Icon, "SanLorShip.EmbeddedResources.plugin-utility.ico")]

// The following GUID is for the ID of the typelib if this project is exposed to COM
// This will also be the Guid of the Rhino plug-in
[assembly: Guid("4AA24A01-E8C0-44EB-9BCF-2125744A0B2F")]

[assembly: Log]

Thanks @farouk.serragedine. That would explain it - the latest C# templates have moved most of the AssemblyInfo to the csproj.