Current questions and answers regarding the map editor.

Check the console more often to identify such errors. It would display "Value was nil when getting global with name 'AddHeroSpells'!", which means the variable AddHeroSpells was not defined. All script functions are variables containing functions that are defined from the Lua scripts that run with the game. If the variable is not defined, then that function does not exist. Then, refer to the manual (or in the script editor, click Ctrl+Space) and find out that there is only the function TeachHeroSpell. Use that instead.

If you follow this principle of error analysis, you won't need help. You can also use the debugging method by Jack_of_Shadows.