Model Builder Error: Not implemented (Exception from HRESULT: 0x80004001 (E_NOTIMPL)) when adding project templates to solution where has one unloaded project.

**System Information (please complete the following information):**
- Windows OS: Windows-10-Enterprise-21H1
- Microsoft Visual Studio Enterprise 2019: 16.11.4
- ML.Net Model Builder: 16.7.7.2150601 (Main Branch)

**Describe the bug**
- On which step of the process did you run into an issue: adding project templates to solution where has one unloaded project.
- Clear description of the problem: If there is an unload project in the solution, will prompt Model Builder Error when adding project on consume page. Reload the project, then can continue adding projects without any error.

**To Reproduce**
Steps to reproduce the behavior:
1. Select Create a new project from the Visual Studio 2019 start window;
2. Choose the C# Console App (.NET Core) project template with .Net 5.0;
3. Add model builder by right click on the project;
4. Select Data classification scenario to complete training;
5. Navigate to Consume page, add one ConsoleApp project;
6. Right click the generated ConsoleApp project to unload it;
7. Back to Consume page to continue adding other project templates;
8. Prompt Model Builder Error: Model Builder Error: Not implemented (Exception from HRESULT: 0x80004001 (E_NOTIMPL)).

**Expected behavior**
No error when adding project templates on consume page.

**Screenshots**
If applicable, add screenshots to help explain your problem.

Reproduzieren Sie den Fehler auf der Seite Consume in Visual Studio 2019 anhand der aufgeführten Schritte, insbesondere nach dem Entladen des generierten ConsoleApp-Projekts. Verfolgen Sie den Ablauf zum Hinzufügen von Projektvorlagen und dessen Umgang mit entladenen Projekten; fertig ist die Aufgabe, wenn zusätzliche Vorlagen ohne den Fehler E_NOTIMPL hinzugefügt werden können.

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