I recently upgraded a DNN 4.x site to DNN 5 (release version, not RC), and I'm having exactly the same problem as the first poster:

A critical error has occurred.
Method not found: 'System.Collections.Hashtable

DotNetNuke.Services.Authentication.AuthenticationConfigBase.get_ModuleSettings()'.

I read through the thread and saw that there might be a way of fixing this by going into the database, etc.  However, I don't have access to the website's SQL files as those are controlled by the hosting people.  Is there a way of fixing the Hashtable error without messing with the database?

Thanks

 I tried using the fix described by the user  "noks" in the second page of this thread, but it's not working.  Basically, his idea is to register a new user, making him superuser in the database, and then clicking on "Proceed to Login".  This way you're able to log into the site with administrative privileges.

However, when I register a new user, I am immediately logged into the site with that user's account.  There is no previous page with a "Proceed to Login" link.

Is there a way to disable that automatic login after registration?  Otherwise there is no time to go into the database and give superuser rights to the new account.

Thanks.

 Problems solved!  I removed the CardSpace, Active Directory, OpenID, and LiveID authentication modules manually by deleting them from /DesktopModules/AuthenticationServices/* and in the database from dbo.Authentication!  I only left the DNN method of authentication and now I can click on Login and log in perfectly as before :)