Hello world app not working

[ryan_chesnut]

I am new to Revit addins, not to coding. I have gone through just about every tutorial and forum I could find, and have not discovered a solution. 

My HelloWorld.dll builds fine and Revit opens with no error. However, when I go to execute the addin, I get a ClassPath not found error. I am suspecting there is a 2024 Revit version mismatch with DotNet version 8. I have recreated this app about 3 times from scratch, and always the same error. 

 

I am using <namespace>.<classname> in my manifest and have implemented the IExternalCommand interface. No code errors.

 

Revit 2024

DotNet version 8 

[jeremy_tammik · Accepted solution]

A Revit 2024 add-in must use the .NET framework 4.8. (Revit 2025 add-ins use .NET Core 8.) Check out the Revit 2024 development requirements here:

• https://help.autodesk.com/view/RVT/2024/ENU/?guid=Revit_API_Revit_API_Developers_Guide_Introduction_...

[ryan_chesnut]

Let me give that a whirl. Thanks for the quick response.

[ryan_chesnut]

Good to go!