Time dependent script

[FatMax]

I´m getting an error with this script:

Code:

-- Changes light depending on time of day date = os.date('*t') hour = date.hour --PIR addr1 = '1/3/3' --Lights val addr2 = '1/1/74' obj = grp.find(addr1) if obj and obj.data and 1 <= hour and hour <= 7 then  grp.write(addr2, 20)     else  grp.write(addr2, 80) end  if not obj.data then  grp.write(addr2, 0) end

The error reads: Attempt to index global ' grp'(a nil value)

Shouldn't the system check the group database for correct datatype and act accordingly..? Or am I misinterpreting the error..?