If this is going to be an ongoing issue which, from your other thread, it appears to be you only really have two options:
1. Enlist the help of 1&1 directly
2. Enlist other help
If 1&1 can't or won't assist dircetly other than suggesting your follow their support documentation, we'll have to go the other way.
If you want me to, I will look at your site structure for you, but to do so I will require user access details and I realise that this is not something you'd give out lightly.
If you would like me to look at this for you, email me using the envelope icon next to my username. I will reply and we can take things from there. The results may be included in this thread for the benefit of other forum users.
I suspect the full and correct path to your web root is not detailed as it should be with your .htaccess setup.
This is a big failing of 1&1 and other large hosts. Smaller hosts often charge more but most of them will happily roll their sleevs up for you if you get nowhere with their support documentation. Some of them will even help you with ASP and PHP if you become badly unstuck. They are now few and far between but such hosts are worth every penny they charge.
I've had to set up quite a few 1&1 acounts for friends and colleagues who were struggling with their phpMyAdmin configuration. 1&1 should really include it by default whent they set up a user account (I do when I host client sites on my own servers) and by doing so they wold be saving their own support services a large chunk of work and increase userbase appreciation of their service. It's even more annoying when you consider that the process can be almost entirely automated from the server admin perspective.
Anyway, I've gone off on one here.
If you'd like me to help in a more dircet manner email me and we can take a a look at things for you. I shan't be offended if you would rather not release your username/password to me.