I downloaded Ubuntu 16.04 to run on VirtualBox (Windows 10 host). I would like to verify the download ([Ubuntu instructions](http://www.ubuntu.com/download/how-to-verify)). From the instructions:

> 
> Tip: On non-Linux systems, you might need to download the GPG tools for this next step. To check if you have the GPG tools installed, run the command `gpg --version` or `gpg2 --version`.
> 
> 
> 

So I downloaded and installed [Gpg4win](https://www.gpg4win.org/).

Ubuntu says to get their public keys from their keyserver:

```
$ gpg --keyserver hkp://keyserver.ubuntu.com --recv-keys "8439 38DF 228D 22F7 B374 2BC0 D94A A3F0 EFE2 1092" "C598 6B4F 1257 FFA8 6632 CBA7 4618 1433 FBB7 5451"
gpg: directory `/home/ubuntu/.gnupg' created
gpg: new configuration file `/home/ubuntu/.gnupg/gpg.conf' created
gpg: WARNING: options in `/home/ubuntu/.gnupg/gpg.conf' are not yet active during this run
gpg: keyring `/home/ubuntu/.gnupg/secring.gpg' created
gpg: keyring `/home/ubuntu/.gnupg/pubring.gpg' created
gpg: requesting key EFE21092 from hkp server keyserver.ubuntu.com
gpg: requesting key FBB75451 from hkp server keyserver.ubuntu.com
gpg: /home/ubuntu/.gnupg/trustdb.gpg: trustdb created
gpg: key EFE21092: public key "Ubuntu CD Image Automatic Signing Key (2012) " imported
gpg: key FBB75451: public key "Ubuntu CD Image Automatic Signing Key " imported
gpg: no ultimately trusted keys found
gpg: Total number processed: 2
gpg:               imported: 2  (RSA: 1)

```

But I'm getting the following error:

[![enter image description here](https://i.stack.imgur.com/FyJtj.jpg)](https://i.stack.imgur.com/FyJtj.jpg)