IsVisibleInDynamoLibrary missing assembly reference?

Hi Everyone,

Whenever I try to use the [IsVisibleInDynamoLibrary(false)] method property, Visual studio shows it in underlined red indicating its missing. I thought I had some references missing so I kept digging around. I found the DynamoSamples file that contains several examples and also noticed I cant build that file because it shows a redline under that property.
Here are my current references.

Capture

Was missing using Autodesk.DesignScript.Runtime;. My bad