Gentoo emerge: "A file is not listed in the Manifest ..."

Params:

Linux moon 2.6.39-gentoo-r3 #4 SMP Wed Aug 31 17:44:51 EEST 2011 i686 AMD Athlon(tm) XP 2000+ AuthenticAMD GNU/Linux

Problem:

When I do emerge <some_package> or upgrade my gentoo, emerge give me bulk of messages like this:

!!! A file is not listed in the Manifest '<package_ebuild>'
also have this warning:
Digest verification failed ...

Solution:

1) Download latest-portage snapshot from some gentoo mirrors:

    > cd /

    > wget ftp://gentoo.kiev.ua/snapshots/portage-20111214.tar.xz

2) Move /usr/portage directory for backup purposes:
     > mkdir /root/temp

     > mv /usr/portage /root/temp/

3) Extracting the portage snapshot:

    > tar xvjf /portage-20111214.tar.xz -C /usr

    > rm /portage-20111214.tar.xz

4) Sync new portage:
    > emerge --sync

That's all now you can update the system or .....

I don't know if this is correct solution, but it working for me.