Das Werkstatt

[PROBLEM]
I'm running a KVM virtual machine host running Debian 7 (wheezy). I tried to connect to it remotely over SSH, using the virt-manager GUI.
I was greeted with the following error message:

Unable to connect to libvirt:

Cannot recv data: ssh_askpass: exec(/usr/bin/ssh-askpass): No such file or directory
Permission denied, please try again.
ssh_askpass: exec(/usr/bin/ssh-askpass): No such file or directory
Permission denied, please try again.
ssh_askpass: exec(/usr/bin/ssh-askpass): No such file or directory
Permission denied (publickey,password).
: Connection reset by peer

Verify that:
- The 'libvirt-bin' package is installed
- The 'libvirtd' daemon has been started
- You are member of the 'libvirtd' group

The message was right: I had been automatically assigned to the "libvirtd" group, but I had to logout and log back in in order for this change to apply.
So: check your group membership! and make sure you're a member of that groups: Unfortunately, this wasn't enough.

[SOLUTION]
virt-manager is trying to open a password-prompt upon login, using "ssh-askpass". In my case, there was no package installed that provided this.

Depending on your system, choose a proper "ssh-askpass" package.
In my case, running XFCE, I chose: