As it seems you are still using an older version, both for the reason you mentioned (.cs file) but it also reads 1.5.8 at the bottom right.
Can you please update to the latest version and let me know if the problem persists?
To do so always make sure to:
1. Delete the original NodeCanvas folder (MAKE SURE you don’t have any of your files in those folders)
2. Update from the asset store
3. Restart Unity