[ubuntu] The disc is already in

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http://ubuntuforums.org – I am getting this errorin ubuntu 12.04 while installing pypar2. The disc is already in from which i was installed the OS. Please some one help me to overcome from this error. :( Media change: please insert the disc labeled 'Ubuntu 12.04.1 LTS _Precise Pangolin_ - Release i386 (20120817.3)' in the drive '/cdrom/' and press enter (Hardware)