Firstly, make sure that the agent is searching for Economy award for the TBP/PIU to LIM leg because it is operated by all-Y aircraft with no J cabin at all.
Failing that, it could be related to the problem with LAN award availability previously reported and discussed in this thread:
http://www.flyertalk.com/forum/ameri...iversal-4.html
See post #48 for a suggestion about asking agent to check an alternative system.
Good luck.
Happy Travels.