Error: not a custom quest

I take it that you are talking about a quest that yoiu are making called Legend of Zelda in the eyes of Dark Link....
Well, I dont know how to break this to you, but I think the quest file has corrupted, which means that you will have to start again or if you are lucky and have made a back up of the file, you will have to start from there.
This happend to me to with my space invasion quest, but I luckly sent a copy of it to ImHoney7 a few days before.
Its just one of those things that happens...
My advise is to always make a back up of your quest and update it every few days.

Are you making this quest, or did you download it from somewhere? I couldn't tell by your message.

I'm was maing this and now I must start over 😞

Can you still open it in Zquest? Are you getting the error message in ZC or Zquest? If you can't open it in Zquest, then it is probably corrupted.

Click Quest -> Header and make sure the Quest Number is set to 0 (zero).