It is a very long script though you only need to read a maximum of 30 lines... (Please excuse how messy it is...)
Errors occur on line 126, 117, and 50 (That I know of)
Apparently, those specific functions think that the function 'GetPlayerData' (On line 58) is nil, even though my tests prove otherwise.
The error occurs only in Online Mode, it works perfectly fine in solo...
What's likely going on is the code is trying to call the function before it gets defined. The easiest way to get around this in a Table is to wait for the member to exist:
repeat wait() until (Self.RemoteFunctions and Self.RemoteFunctions.GetPlayerData)