If you are interested in resolving the same issue in Opera 30.0.1835.88 (or earlier), please proceed here.
In Opera 30.0.1835.88 (and earlier) there was a way to allow usage of outdated plugins (e.g. old version of Adobe Flash Player) by adding --allow-outdated-plugins argument to an Opera launch shortcut.
But starting from version 30.0.1835.125 the browser seems to ignore this key and it blocks startup and usage of outdated plugins.
Is there a way to overcome that and allow usage of outdated plugins?
P.S. There is no need to post remarks about importance of usage of updated versions of plugins, security and so on. For example, there is a plenty of stone age machines, where the modern versions of Adobe Flash are just unusable, whereas the old ones work acceptable.