you need direct access to the database to perform the following steps:

• ensure, that registration is not set to none, if necessary alter portal settings directly in the database to value 2.
• register as a new member
• go to aspnet_membership table and copy password and password salt from new user to host.
• you can now login as host and alter others' accounts

OK... Got the b***h solved and can login now...

While nothing else worked at all, the problem was solved by doing this:

1. Create a new user.
2. In MS SQL Server find the ApplicationId that the user is in.
3. Update all affected logins to use the new ApplicationId as in the following SQL script

UPDATE aspnet_Membership
Set ApplicationId='NewUsersApplicationId'
where ApplicationId='OldUsersApplicationIdThatDoesntWork'

UPDATE aspnet_users
Set ApplicationId='NewUsersApplicationId'
where ApplicationId='OldUsersApplicationIdThatDoesntWork'

UPDATE aspnet_Roles
Set ApplicationId='NewUsersApplicationId'
where ApplicationId='OldUsersApplicationIdThatDoesntWork'

I hope that helps some poor soul out... (It cost me way too much time to get that.)

Ah - right - symptoms... You can't login and you get an "Object not set to an instance of a blah blah blah yadda yadda yadda..." error message.

Cheers,

Ryan