1. it has to be two lines, on your first line have common drops second line rare drops
2. the id 3590 is for steel dragon not Ice stryworm
3. you might be using spaces instead of tabs (if you get compiling error)
follow this format
#Name (found in NPC file)
MONSTERidropRate (for second line drops) itemid:amount (tab) itemid:amount (enter)
itemid:amount