juju deploy: series does not match

What is your host series? Precise? Trusty? It's likely that the default series does not match so it's trying to deploy the incorrect charm type.

Try: juju deploy --to 0 cs:precise/juju-gui if it's precise or "cs:trusty/juju-gui" if it's trusty.

Three things to check:

1. Is there a default-series setting in your $HOME/.juju/environments.yaml for your environment named "manual"? If not, I think "precise" is still the default.
2. Immediately after juju bootstrap, run juju status and see what's the machine 0's "series" (e.g. "series: trusty"). The charm you're trying to deploy must match that series.
3. After running juju deploy juju-gui --to 0, you'll see a message like Added charm "cs:precise/juju-gui-98" to the environment. If the series on the machine did not match the charm series, you'll also get an error like ERROR cannot assign unit "juju-gui/0" to machine 0: series does not match.

So, you either deploy with explicit series, e.g. juju deploy cs:trusty/juju-gui --to 0, specifying a series matching machine 0's series; or alternatively, set "default-series: trusty" before bootstrap.