My First Revit Plug-in - "Object reference not set to an instance of an object" Problem

[Anonymous]

Hello, 

I have started My First Revit Plug-in tutorial: https://knowledge.autodesk.com/support/revit-products/learn-explore/caas/simplecontent/content/lesso... and I have problem in the lesson 1. 

I am working on Revit 2021 trial version and Visual Studio 2019.

After writing an AddIn Manifest and saving it in the right folder I run Revit and after selecting "External tools" the error shows up - screens. 

Please help and ask if you need more info 🙂

[Anonymous · Accepted solution]

Thanks to this video: https://www.youtube.com/watch?v=ulvaJP4kjKE I realized that I need to open some existing Revit model before selecting External tools. They forgot to mention that in the tutorial or I just missed that 🙂