I just reloaded an autosave where I had just completed research on Heroes. I was unable to recruit any level 5 Heroes or go on level 5 Hero Quests as indicated in the tech tree. This is not normally a problem, therefore, the only thing I can think of is that it must have something to do with the autosave. I loaded the game I saved after the autosave, and I was able to recruit level 5 heroes and go on level 5 quests as per normal.
