I search a lot about this problem, but all the solutions I found did not solve my problem. I installed Linux Mint 17 with mate desktop in a virtual machine. After the installation, I wanted to update the packages but after running
apt-get update
I get the following error:
E: GPG error: http://archive.ubuntu.com trusty Release: The following signatures were invalid: NODATA 2
The solutions I found in https://askubuntu.com/questions/104213/gpg-invalid-signature did not solve it.
I think the problem is that the computer is behind a proxy. I tried all the different proxy settings, but the error still exists.
Thanks