Error installing "could not get lock..."

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Error installing ROS on Ubuntu 11.04

Error in step 1.3:

Ign http://security.ubuntu.com natty-security/universe Translation-en Get:7 http://archive.ubuntu.com natty/restricted Sources [4,104 B] Fetched 1,024 kB in 5s (194 kB/s)
E: Could not get lock /var/lib/dpkg/lock - open (11: Resource temporarily unavailable) E: Unable to lock the administration directory (/var/lib/dpkg/), is another process using it? ted@ubuntu:~$ sudo apt-get install ros-diamondback-desktop-full E: Could not get lock /var/lib/dpkg/lock - open (11: Resource temporarily unavailable) E: Unable to lock the administration directory (/var/lib/dpkg/), is another process using it?

Then similar error in step 1.4 (in the install instructions):

sudo apt-get install ros-diamondback-desktop-full

From the terminal, I get the error:

Unable to lock the administration directory (/var/lib/dpkg/), is another process using it?

Help me please? :)