For future reference, if you don't want to use a program to remove invalid install entries, you can find them in the registry as subkeys under HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Microsoft\Windows\CurrentVersion\Uninstall or HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall depending on the type of Opera install you did. The keys will start with "Opera" in their names. You just delete the keys for the versions that are invalid.
