Error extracting metadata for project : An item with the same key has already been added

**DocFX Version Used**: 2.33

**Template used**: `default`

**Steps to Reproduce**:

Paths have been anonymized to protect the innocent.

1. Execute `docfx metadata C:\Users\someuser\Code\SomeProject\Module\SomeLibrary.Shared\SomeLibrary.Shared.vbproj -f`

**Expected Behavior**:
Successfully generates metadata

**Actual Behavior**:
Metadata generation fails with the following error:
```
[18-03-19 07:58:56.263]Info:[ExtractMetadata]Generating metadata for each project...
[18-03-19 07:59:04.842]Error:Error extracting metadata for C:\Users\someuser\Code\SomeProject\Module\SomeLibrary.Shared\SomeLibrary.Shared.vbproj: Error extracting metadata for project "C:\Users\someuser\Code\SomeProject\Module\SomeLibrary.Shared\SomeLibrary.Shared.vbproj": An item with the same key has already been added.
```

**Notes:**
This is the first time trying to run docfx on our project. I saw the same error on other VB or C# projects. I tried earlier versions and saw similar/additional errors. I also see the same error when using a solution that contains the projects.