ruario at my Opera community (an Opera employee) has made research and he determined that at least for Opera deb file, the issue is with lzma not being present in default Ubuntu install. Here's the full discussion and ruario's research's conclusion:
http://my.opera.com/community/forums/topic.dml?id=1124872&t=1318873023&page=1#comment10564932 -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/858246 Title: Software center cannot install opera deb file: Internal Error To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/software-center/+bug/858246/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs