Presumably you're using Opera 36.
Unfortunately as the current Opera is 43, 36 will now be considered to be very out of date by some sites, which are annoyingly starting to actually block old versions of all browsers with no means to override this.
Rather a pain if you're stuck on an old operating system for any reason.
I think probably all you can do is find an extension which will spoof the browser user agent string, so the site thinks you're using something newer.
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