After updating to J3.1 from J2.5.10, my default registered user account cannot access private area of the site. I am using a Rocket Theme, but I tried with Beez and Atomic and I have the same behavior. I can use the admin account from the front of the site and login with no issues at all.
Never joined OSTraining... but using Joomla since 1.0 and have not really found anything that I could not figure out on my own, with web searches, or forums before now. If I do not get a answer from somewhere by the first of the week I may contact them.
Follow up... Did contact OSTraining and they fixed the problem for me. The Joomla update manager (migrating from 2.5.10 to 3.1), mangled the assets table in the database. They realigned everything and it works fine now...
Just wanted to follow up... You were right, OST is VERY good.