This isn't a tool limitation but a license limitation. You will need to contact Cadence to verify this but the Auto Router which comes bundled with OrCAD PCB only supports 6 routing layers and does not support Blind and buried vias during auto routing, among other functionality. I believe the performance options may give you more functionality but it depends on which licenses you have. Check out pages 6 thru 10 of the below PDF Document which describes the different tool suites/levels and what functionality you should expect. Like I said it is probably best to contact Cadence directly to discuss your options.
Hope this helps,Mike Catrambone
Again, Thank You Mike for you time and help!
No problem, anytime. Please don't estimate to post questions to the forum. We have a lot of knowledgeable folks subscribed that are always willing to help out.