Problem with ppa:mapnik/nightly-2.3

Hi, 

I receive this error:

```
Cannot add PPA: 'ppa:mapnik/nightly-2.3'.
Please check that the PPA name or format is correct.
The command '/bin/sh -c add-apt-repository -y ppa:mapnik/nightly-2.3 &&       apt-get update -y &&       apt-get install -y libmapnik libmapnik-dev mapnik-utils python-mapnik' returned a non-zero code: 1
```

Any idea about how I can fix it? 