You need to use Player.X_Pos
instead of Player[X_Pos]
and so on.
The brackets notation will interpret "X_Pos" as a variable and try to access taht key instead (the reason for the error is that undefined variables default to null)
t = {a = 17}
print( t.a ) --dot notation is simpler
print( t["a"] ) --bracket notation expects a string
key = "a" --that string can be from a variable
print( t[key] )