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An update or reinstallation of the phone's current software update should fix this. You can update the phone with Nokia Suite.
To make sure you won't lose the data on your phone, make a back up first. Click on Tools > Back up to do this. Once you've made the back up, click on the green arrow in Nokia Suite where you will be able to update or reinstall the current software of your phone.
When the phone has rebooted, the application will work again and will be updated to the latest version of Opera mini.
Do let me know how you get on.