I don’t know what the problem might be, as I overburn all the time with the latest Nero version and the popup comes up every time. 85-99 minutes is an extreme overburn that could normally only be done with 90 to 99 minute discs. I never use these discs because of their low quality and compatibility problems.
My method for overburning is to first test the overburn capacity of a given disc with CD Speed, and then set the Nero preferences just a tad below the absolute capacity of the disc. I have pretested my different 80 minute blanks, so I know the capability of each. Depending on how much capacity I need, I select the blank that has the best fit.
In your case, hardware may be involved. What burner and model are you using? I would suggest that you try CD Speed first to test the capability of the burner/disc combination.