I ran into the same issues during install. The providers for roles can come from both machine and web.config, however web.config overrides machine.config. Unless you are using a role manager that you have placed into machine.config, add a <clear/> as the first item in the list of role providers to avoid these conflicts
The <clear/> saved the day! I put 1.8 into production from my local server starting at midnight .. the birds were singing and the sun was coming up when I hit on your suggestion and got it going on the live server. Although there are other issues and I've reverted to the old non-nop site for a few days. The <clear /> did it. Thanks