non hyundai tpms sensor

I installed aftermarket snow tires with tire monitors - for the first two days all was fine then the TPMS warning message came on and continually dings every 15 seconds. I had it checked and reprogrammed and the warning has not stopped. Can anyone help with this?

SO i just got a set of wheels and tires from Tirerack and obviously had the tpms option installed. They are Continental branded sensors, but my car saw them immediately, no "initialization" needed. Hope this helps those who may have been wondering.