Got a new Garmin today. a Garmin Forerunner 405
with HRT and a chest strap HRT

i been using a Garmin 500 and works great. the chest strap works well

Problem is the chest strap i got with the 405 is not working. both my monitors are not picking it up at all.
so i use the strap my 500 came with and both 405 and 500 pick it up

what could be wrong with a HRT chest strap not working, as its brand new.
suggestions thanks