@hucker In "C:\Users\yourusername\AppData\Opera Mail" (if I remember correctly) is where operaprefs.ini is at.
That's also where the crt.dat files and trust.dat files are at. You should be able to delete optrust.dat to get the dialogs again to start approving from scratch. Not sure if it will help though.
You can install Opera 12 without interfering with Opera Mail. There's a choice in the Opera 12 installer to even make a standalone installation so you can just install it to a folder on your desktop. data will be in the "profile" folder in that folder on your desktop. Would be best to do the standalone installation so it doesn't make changes to the registry.