Which opera related entry is in your sources.list and did you add the archive key?
sources.list entry:
Code:
#Third Parties Repos
#The Opera .deb Repository
http://deb.opera.com/opera/ stable non-free
Extra action to take after adding the opera entry:
Code:
wget -O - http://deb.opera.com/archive.key | sudo apt-key add -
You need to do this just once.