Ubuntu update Error Again!!!!

This time is invalid Signature

I have headache for hours why it's say invalid signature eventhough I tried set default keyring in the repository. But after googling for some keyword I just found out that it's a BUG!!! Great!!! It's problem with the ISP's cache so how to AVOID it. Follow the instruction below.

use the same apt-get update but put one of these options after update

$ sudo apt-get update  -o Acquire::http::No-Cache=True

or

$ sudo apt-get update -o Acquire::BrokenProxy=true

Then it's working again!

Ref: Launchpad.net , Ubuntuforums.org