It could be in several reasons: 1. You lost wifi connection. Just reconnect. 2. Server where package is not working now. I had this problems with Extras-development yersterday for several ours. Just wait and try few hours later. 3. Most possible you didn't update before downloading new package. I recommend you: a) open App Manager; b) Press Update; c) install new soft. Update in Linux (used "apt-get update" command in xterm under root) update information about repository. If package was changed in repository your App.Manager don't know it until update. After Update information for repository you can upgrade upgradeable packages ("apt-get upgrade"). In linux update and upgrade it is 2 different steps. Steps to do: 1. reconnect to inet; 2. Press Update in App.Manager; 3. If you have some packages to update than update them. 4. Install package which you want 5. If you will get this message again then wait for several hours and try again
OK. forget my DNS idea then. it worked for me.