when no points is set - default value will be "false"
and you cant add 1 to "false".
local playeraccount = getPlayerAccount (source)
local playerpoints = getAccountData(playeraccount, "DD.Points")
if (playerpoints==false or playerpoints==nil) then playerpoints=0 end
setAccountData (playeraccount, "DD.points", playerpoints)
you also should check if playeraccount is valid!