Comment 12 for bug 858246

The problem is that the data.tar file within the Opera Debian package is lzma compressed. Since /usr/bin/lzma is not present on Ubuntu "Oneiric Ocelot" 11.10, Software Center cannot open the file.

However, other utilities such as dpkg and apt can open the package and install it without any issue because they use /usr/bin/xz to open lzma compressed files. Indeed if you create /usr/bin/lzma as a symlink to /usr/bin/xz then software center can open the Opera package as well.

This can be fixed in two ways, either the /usr/bin/lzma symlink should be provided by the xz package for backwards compatibility (in fact that is good idea anyway as xz is just a continuation of lzma and other distros do this) and/or Software Center should be updated to use xz when lzma is not present.

http://my.opera.com/community/forums/findpost.pl?id=10564932