That probably is an issue to do with the ISA proxy setup in your organization. I had the same issue when configuring a virtual server for my organization.
Open the terminal. In the terminal type in the following command:
sudo nano /etc/apt/apt.conf
This command is meant to open up the apt.conf file and make it available for configuration. If you are prompted for your password, enter it.
Add the following lines into the file:
Acquire::http::proxy "http://[username]:[password]@[proxy_address]:[port]";
Acquire::https::proxy "https:// [username]:[password]@[proxy_address]:[port]";
Acquire::ftp::proxy "ftp:// [username]:[password]@[proxy_address]:[port]";
Acquire::socks::proxy "[username]:[password]@[proxy_address]:[port]";
Where: username - Your proxy username password - Your proxy password proxy_address - The address of the proxy server port - The port on the address server through which traffic is allowed
Save the apt.conf file. Try and run the apt-get command and it should give you something similar to this
sudo apt-get install [package]
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following extra packages will be installed:
………
Do you want to continue? [Y/n] y:
If you see this response, that means that the package is ready to install.