On my Win7 Computer I have the same problem, the Error message only appears seldomly. Opening Opera a window opens, I can use full screen or smaller for a few seconds, then the window closes. This happens in a 10 sec Rhythm repeatedly. The proceesor speed runs to 100 % during the open phase. I am the only user and administrator. Yesterday I deleted Opera completely which was not without problems maybe because I use it since about 25 years. It was situated in the main "program files" compartment. I installed the actual version now in the "users" compartment. The problem has not changed, Funny, my attempts to activate my new Opera membership also failed because the link tried to open Opera.
