I got above error when i try to create unit test for private method IsConnectionOK.
I remembered I manually removed the Test Reference folder in test project by deleting below xml node from .csproj file. is it relative? I added back and then tried "Create Unit Test", it works now.
<ItemGroup>
<Shadow Include="Test References\DataLoader.accessor" />
</ItemGroup>
DataLoader is the class name where method IsConnectionOK resides.