Every few months when trying to install something on my personal Gentoo Linux server, I run into this interesting error. In the latest case, I was running 'emerge mod_php' which resulted in :-
!!! CATEGORY info missing from info chunk, aborting...
So far, the only fix for this seems to be :-
rm -rf /var/tmp/portage emerge mod_php
Something that might make a difference (it is too soon to tell), is to edit /etc/make.conf and ensure that the FEATURES setting does not contain "buildpkg".