I think you need to try and remove it complete from your system, it sounds like it is referencing the wrong version (or that it doesn't realist it's all been removed.
Before you proceed with removing Opera, it is important that you know
where Opera stores its settings. In Opera, go to Help > About Opera.
Under "Paths" in the About Opera page, look for the path to your
preferences - the Opera6.ini file. Take note of this path, as it will
be needed to completely remove Opera from your system.
- Uninstalling Opera
To uninstall Opera, open the Control Panel from the Start menu in
Windows. In the Control Panel, open "Add or Remove Programs", and
locate Opera in the list of installed programs. Click "Remove" to
Please note that this will not remove user created files and settings.
- Removing user created files
In order to completely remove an Opera installation, the following
directories must be removed after performing a normal uninstall:
The folder you installed Opera to.
The Opera settings folder.
If you chose not to use separate settings for each user when
installing Opera, you will only have to remove your Opera installation
folder. To find out if this is the case, look at the location of the
file Opera6.ini, which you found earlier, and compare it to the path
to your main Opera installation folder.
If the location of the Opera6.ini file is different from the location
of opera.exe, you are using separate settings for each user, and will
have to delete two folders manually.
Before proceeding, you may wish to take a backup of your files in case
you wish to install Opera again:
To remove the remaining files on your system, simply delete the Opera
installation folder. If the Opera6.ini is separate for each user (in a
different location than opera.exe, make sure you delete the folder
where this file can be found as well.
I have also seen people recommend this tool called Revo.
Source for tool recommendation