Def's in application.rb are not visible in other files in ap

Hello,

I have this weird situation, I have authenticate def in

application.rb, and all classes, views in my project can use this
defs, but one day, I have an error about authenticate def not found, I
don’t know what happened but that def was unavailable to rest of
project.

Have somebody experienced something like this?, how can be solved?

Thank you