Problems with my anti theft device on my 2002 vw golf?

so back story... my key flew off my lanyard and broke. ilost my transponder... bought a new one online. put it in my key and had a locksmith program it. ok. so recently ive had a problem with my anti theft. and sometimes ill have to turn the key off and on a couple times and it works. other times it wont work and ive replaced the transponder antenna that goes around the ignition. and it works for a bit no problem... then boom. same problem... so what could it be? do i need to replace my computer?