Why can't my data stores be accessed?

I have this code put into a module script in the replicated storage:

local DataStoreService = game:GetService("DataStoreService")
local playerData = DataStoreService:GetDataStore("PlayerData")

Everytime the game is started up, however, it keeps having this error: "Data store can't be accessed from client." Why does it do this? API Servers are already enabled.