You should only install apps from the PCLinuxOS repository, i.e. via Synaptic package manager. When you install from outside sources, whether it be an RPM you found on the net or from source code, you start on the road to a problem or problems and could completely bork your system; plus you render your system officially unsupportable. This does not mean that no one will want to help, but rather that you will have made it near impossible, if not impossible to help you. The outside RPMs may call for non-PCLinuxOS-standard dependencies or configuration, which will sooner or later cause trouble. I'm not going to try to explain the problems of source code installation.
This may be a "workaround" for your current problem >>> Open Synaptic > remove opera completely > close Synaptic >
Open Root PCmanFM (File Manager Superuser) > navigate to /usr/share/applications > look for the opera.desktop file > right click it and choose Rename > rename to opera-11.5.desktop > close Root PCmanFM >
Open Synaptic > install opera.
If all goes well, you will have 2 entries in the menu for opera.
Otherwise, you may want to back-up your data and reinstall PCLinuxOS.
One further word, if you will. When you request help, do not hold back information. The more information you provide, the better. Something that may seem trivial/unimportant to you may be a vital clue in figuring out what has gone wrong. It is better to give too much information than not enough.