Music Track Doesn't save Custom music

Well i’m using DDDK Dungeon Defenders Development Kit to make a map. i was going to use custom music i made an “PlayBuildMusic” Remote Event like i should to get it to work. saved it and it works. made a Play Music Track,saved and it worked. Inserted the custom music and it gave “Graph is linked to object in external map package.” So i know what the problem is. but i don’t know WHY its doing this.

anyone know the answer to this? :l i tried looking for the answer but none of them helped me.