I dislike 1and1 web hosting when it comes to Drupal sites, but several of my clients use 1and1 so I make it work. The problem is needing to do additional configuration such as:

adding the following to the .htaccess file ro force PHP 5 rather than the default v4.:

AddType x-mapp-php5 .php
AddHandler x-mapp-php5 .php

Another problem is a memory limitation…. so you need to include a php.ini file:

Here is the code in my PHP.ini, which is placed in the same directory that Drupal runs.

register_globals=off
upload_max_filesize=20 M
max_execution_time=300
memory_limit=40 M
post_max_size=20 M
SMTP:localhost