While trying to open an old grasshopper file created in Rhino 4 with Grasshopper in Rhino for Mac, I get an IO error message with the associated log message:
“Object reference not set to an instance of an object”
I figured that there were some components in the file that were obsolete, and found one that looked like it was obsolete. I deleted that component (which broke a plane down into its components, which seemingly had been replaced with DePlane). I erased all instances of the component, reserved the file, and the new file still failed to open in my copy of Grasshopper in Rhino for Mac.
I’m at a loss at what else might be causing this error.
The file opens without problem in Rhino6 Windows, although because it references a brep and some curves those are missing and some components don’t work. But there’s no errors trying to open the file.
I saved the file without changing it, maybe this one opens correctly? You’re right that some of the components are obsolete, but that shouldn’t matter. You can replace them if you want, but the old components are still there and fully functional.