I tried to install bumblebee on Ubuntu 12.04 LTS by following steps on ubuntuwiki site. But when i used this code:

sudo add-apt-repository ppa:bumblebee/stable && sudo apt-get update

this output came out:

Executing: gpg --ignore-time-conflict --no-options --no-default-keyring --secret-keyring /tmp/tmp.q0zzLiXVT3 --trustdb-name /etc/apt/trustdb.gpg --keyring /etc/apt/trusted.gpg --primary-keyring /etc/apt/trusted.gpg --keyserver hkp://keyserver.ubuntu.com:80/ --recv 46C0364A882F14F899448FFCB22A95F88110A93A gpg: requesting key 8110A93A from hkp server keyserver.ubuntu.com
gpg: key 8110A93A: "Launchpad PPA for Bumlebee Project" not changed
gpg: Total number processed: 1
gpg: unchanged: 1
E: Type 'ain' is not known on line 3 in source list /etc/apt/sources.list.d/bumblebee-stable-precise.list
E: The list of sources could not be read.

There´s also the same problem message when I try to run the update center.

´E:Type´ain´ is not known on line 3 in source list /etc/apt/sources.list.d/bumblebee-stable-precise.list, E:The list of sources could not be read., E:The package lists or status file could not be parsed or opened.´

I don´t know what to do since I´m a newbie at Linux. Thanks in advance, Samuel.