Manually Edit the Configuration File

Open the file /etc/apt/apt.conf by pressing Alt+F2 and running gksu gedit /etc/apt/apt.conf. Don't worry if it is an empty file. Add these lines into the file and save it:

Acquire::ftp::proxy "ftp://Username:Your_password@domain:port-no/";
Acquire::socks::proxy "socks://Username:Your_password@domain:port-no/";
Acquire::http::proxy "http://Username:Your_password@domain:port-no/";
Acquire::https::proxy "https://Username:Your_password@domain:port-no/";

Replace username by the username assigned to you and the password by your password, domain by the domain of your proxy like 10.1.101.150, which is my college's proxy address and by the port no like 3128 or the one which you have, if you do have these parameters assigned to you, else leave out username and password and also the characters: : and @ upto domain.

To add proxy authentication parameters to other applications, have a look at this answer to a similar question.

Use the Easy GUI Utility

Another way to add this information is by going to System Settings → Network → Network Proxy then add your proxy settings and click on Apply Settings System-wide. This will add the proxy settings but you will have to add the user-name and password manually using the command-line method described above.

I just erased my account from Empathy so I could help you out. When I first started I had the same problem. I hope this helps you.

Log in to Facebook in your web browser, & click on the little gear in the top right corner, & click Account Settings. Under General, it will say username in there (your will look different than the example I provide) it will say something like:

http://www.facebook.com/JohnDoe

After the last "/" is the thing you need to input in to Empathy (it is case sensitive), so in my case I would put in JohnDoe

Then type in your password for Facebook, & then click Log in.

I hope that helps, because that is the best I can help. If that doesn't fix it someone else might be able to help you out :-)