Iolo System Mechanic Pro contains a large number of specialized "tool" and "protection" modules, any number of which can interact "unpleasantly" with otherwise good software on a system. The AV module (using heuristic methodology) is just one possible problem cause. Depending on what you may have directed SMP to do after installing it, other areas of concern are its: registry cleaner, privacy cleaner, Memory Mechanic RAM optimizer, and Stability Guard auto-system-optimizer/protector. The various cleanup modules have the capability of removing files and registry entries, and of course can damage a software installation in several ways if misdirected somehow. The various "guard/shield" modules have the capability of blocking certain system operations needed by various installed software, which can prevent that software from loading or running correctly if the software acts in a way pre-defined by SMP's internal rules as being a risk.
As with any such comprehensive "cleanup" and "protection" tool, there are a myriad of possible problem areas that can arise. If you can totally disable all of System Mechanic's functions, check to see if Opera will then load. If it does, try enabling/turning-on the SMP functions one at a time to see if one blocks Opera. If Opera doesn't load even with SMP fully disabled, then the Opera installation (including registry entries) may have been damaged by some SMP clean up operations.
At the end of the day, you might be best served by consulting with the System Mechanic support group.