In my view, this is a terrible problem. I have
written privately to Cocoa Spud to see what he
thinks. I will let you know what we conclude.

65002 is MAX_QUEST_STAGE+1, and is returned by the quest lookup function
when it cannot find the asked for quest.

We store all quests in the saved game file. So what's probably happening is that you play a design and save the game. Then use the editor to add new quests and events that reference the quests. Now play the edited design and load the saved game and the old quests replace all of the new ones. When you trigger one of your new events, it tries to reference a quest that was removed by loading the saved game.

I think we can fix this problem. Looking at the code it appears that the same problem exists for special items and keys too.

Do you understand what has happened here? I will say what
I understand.

There are two sets of files: 1)The Design and 2) The SaveGame.
When you edit a design you naturally edit the 'Design' files.
So, if you add a quest, you add it only to the 'Design' files
and not to any 'Savegame' files that are lying about.

When you save a game, all the quests are written to the 'Savegame'
files. When you load a savegame, the program discards any
quests that are in the 'Design' files and loads all quests from
the 'Savegame' files. So any quests that you added to the 'Design'
files after saving the game will not be there!!!!

CocoaSpud tells me that he is going to change the behaviour of
the program when it loads a savegame. Instead of deleting all the
quests from the 'Design' files and replacing them with the quests
from the 'Savegame' files, he will update the 'Design' file quests
with the 'Savegame' quests. If the same quest exists in both
files then the 'Design' quest will be replaced with the 'Savegame'
quest. If the quest exists in only one of the files then it, of
course, will be used.

There are some additional, rather technical, details that make this
possible....a little foresight by CocoaSpud several years ago has
paid off.