error in function onAttack

[xupenba]

hi guys, I made ​​a script and el lo ta giving error:

function onAttack(cid, target)

if(getPlayerStorageValue(target, 7999) == 1 and getCreatureSpeed(cid) >= 0) then
doChangeSpeed(cid, getCreatureBaseSpeed(cid))
return true
end
end

error:

[31/07/2013 18:46:45] [Error - CreatureScript Interface]
[31/07/2013 18:46:45] data/creaturescripts/scripts/sagaone.lua: onAttack
[31/07/2013 18:46:45] Description:
[31/07/2013 18:46:45] (luaGetCreatureStorage) Creature not found

thank you for your attention..