I realize this is about a week late but with the holiday season I didn't get a chance until today to get to the root of the problem.
A number of people ran into a problem when they did a fresh install or an upgrade and installed either the Active Directory provider, the Cardspace provider, or both. The providers installed fine but when the user went to login they got an error (Method not found: 'System.Collections.Hashtable DotNetNuke.Services.Authentication.AuthenticationConfigBase.get_ModuleSettings()'.).
One of the changes for DNN 5 was that the settings for the providers was moved from the ModuleSettings table to the PortalSettings table. The Cardspace provider has not been updated to refer to the PortalSettings table so that's why it's causing the error. The AD provider was updated but I discovered a bug shortly before the release of DNN 5 that caused an error when settings were applied to the provider. This same bug evidently also affected the core Login control. A new version was submitted to the DNN Release Tracker but it didn't get passed through in time to make the final release.
So, how do you get around this error? It's actually quite easy. If you open the Authentication table in the database and remove both the lines that reference Cardspace and ActiveDirectory you'll be able to login without a problem.
I did test installing DNN 5 by replacing the broken version in the in the DNN install package with the AD provider currently in the Release Tracker and did not run into any errors when clicking Login.
If you have upgraded a production site to DNN 5 and Active Directory is a requirement then you can get the version that's currently in the tracker from my personal site (http://dnn.gmss.org).
We're currently working on getting the Cardspace provider updated.
My apologies for any problems the two providers have caused any of you.