Runtime Error in Help Desk

So I am very new to mapping and such, and I'm working on my first relativley big map and I wanted to add a moving mystery box. So I put the ugx_mystery_box prefab in instead of the regular treasure_chest and did the whole Enter Prefab and gave the trigger key 'script_noteworthy' value 'start_chest' and on the second mystery box 'chest1' as that's what I've seen you were meant to do. Now when I launch my map I am encountering a script runtime error.

Code Snippet

Plaintext

******* script runtime error *******
pair 'default_treasure_chest_' and 'undefined' has unmatching types 'string' and 'undefined': (file 'maps/_zombiemode_weapons.gsc', line 730)
 self set_hint_string( self, "default_treasure_chest_" + cost );
                                                       *
Error: called from:
(file 'common_scripts/utility.gsc', line 586)
  entities ] thread [[ process ]]();
                                  *
Error: called from:
(file 'maps/_zombiemode_weapons.gsc', line 582)
 array_thread( level.chests, ::treasure_chest_think );
 *
Error: called from:
(file 'maps/_zombiemode_weapons.gsc', line 11)
 treasure_chest_init();
 *
Error: called from:
(file 'maps/_zombiemode.gsc', line 59)
  maps\_zombiemode_weapons::init();
  *
Error: called from:
(file 'maps/infected_street.gsc', line 119)
 maps\_zombiemode::main();
 *
Error: started from:
(file 'maps/infected_street.gsc', line 9)
main()

As I had said I am new to mapping and don't understand what I can do to fix this. Any help is appreciated.

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Runtime Error