While trying to install new software on a freshly installed Ubuntu 9.10 (Karmic Koala) using the Ubuntu Software Center, all installable softwares were showing a “not available in the current data” message. The solution is to do a “sudo apt-get update” in your terminal.
However, “sudo apt-get update” might also gives you error messages such as “Err http://au.archive.ubuntu.com/karmic…. Unable to connect to au.archive.ubuntu.com” which means the server where you’re getting updates from is currently down.
In this case, you can change where you get updates from by going to System > Administration > Software Sources and select “Main Server” in the Download From dropdown. Rerun “sudo apt-get update” from the terminal and you should be good to go this time.