I upgraded from 4.5.3 to 4.5.5 and I am now unable to login as host or admin.

Message: Login Failed, remember that Passwords are case sensitive.

I made sure to backup web.config, copied over my connections and machine keys.

What are my options?

Reinstall? - Will I lose my data?

I ran into the same issue after upgrading a DNN site.  Turned out to be part of the database upgrade that didn't complete.

In my case I noticed that 'exec dbo.GetModuleByDefinition @PortalId = 0, @FriendlyName = N'Authentication'' didn't return any data.

The problem was that moduledefinitions table still had a value of 'Windows Authentication' for the login module and the above procedure was looking for 'Authentication'.

select * from modules where moduletitle like '%Authentication%'  order by moduletitle

update moduledefinitions set friendlyname = 'Authentication' where moduledefid = #ofyourmoduledefid