Welcome to FT.

The purpose of the challenge is to provide a quick way to status as a means of ensuring future travel patterns, i.e. earning status the "real" way. Aa have begun cracking down on folks who abuse the challenge system (consecutive year challenges) and this is what you're running into. Obviously, serial challenges defeat the purpose of the challenge system.

The way around this is to fly 50K miles and earn PLT status in the normal way.

Cheers.