I figured out the issue, I was using a really old version of game maker. I updated it and it worked.
Also i have another question. Am i able to convert a ds map into an array to save and back to a ds map? Its just that was the way i learned to handle quests trees so its what I'm used to using to store them.
Thank you
Glad you sorted your problem out! Yeah, this was written for GameMaker Studio 2 V2.3+, anything older than that won't work.
To answer your question, yes, you can do that using json_encode to turn it into a struct. Then, when loading it in you can read through the struct's values and re-create the DS map. (note that you cannot directly set the DS map as a value in SSave, so when re-creating it you will have to store the DS map in a variable somewhere else).
Hope that helps!!