I get the following error message when I run synaptic and I can't install any programs

SystemError: 
W:Ignoring file 'getdeb.list.bck' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension, 
W:Duplicate sources.list entry 'http://extras.ubuntu.com/ubuntu/ precise/main i386 Packages (/var/lib/apt/lists/extras.ubuntu.com_ubuntu_dists_precise_main_binary-i386_Packages), 
W:Duplicate sources.list entry  'http://extras.ubuntu.com/ubuntu/ ' precise/main i386 Packages (/var/lib/apt/lists/extras.ubuntu.com_ubuntu_dists_precise_main_binary-i386_Packages), W:Duplicate sources.list entry 'http://extras.ubuntu.com/ubuntu/ precise/main i386 Packages (/var/lib/apt/lists/extras.ubuntu.com_ubuntu_dists_precise_main_binary-i386_Packages), 
W:Duplicate sources.list entry ' 'http://extras.ubuntu.com/ubuntu'/ precise/main i386 Packages (/var/lib/apt/lists/extras.ubuntu.com_ubuntu_dists_precise_main_binary-i386_Packages), 
W:Duplicate sources.list entry' 'http://extras.ubuntu.com/ubuntu/ precise/main i386 Packages (/var/lib/apt/lists/extras.ubuntu.com_ubuntu_dists_precise_main_binary-i386_Packages), 
W:Duplicate sources.list entry 'http://extras.ubuntu.com/ubuntu/ precise/main i386 Packages (/var/lib/apt/lists/extras.ubuntu.com_ubuntu_dists_precise_main_binary-i386_Packages), 
W:Duplicate sources.list entry 'http://ppa.launchpad.net/ubuntu-mozilla-security/ppa/ubuntu/ precise/main i386 Packages (/var/lib/apt/lists/ppa.launchpad.net_ubuntu-mozilla-security_ppa_ubuntu_dists_precise_main_binary-i386_Packages), 
E:Encountered a section with no Package: header, 
E:Problem with MergeList /var/lib/apt/lists/packages.rssowl.org_ubuntu_dists_precise_main_i18n_Translation-en, 
E:The package lists or status file could not be parsed or opened.

I'm new to Linux so please help me out .