Today's your lucky day, I happen to know how to fix this error.
In the creaturescript, try changing this line:
doCreatureSetStorage(cid, KILLSSTORAGE_BASE + id, getCreatureStorage(cid, KILLSSTORAGE_BASE + id) + 1)
with:
local storageUpdate = getPlayerStorageValue(cid, KILLSSTORAGE_BASE + id)...