This issue had been bugging me forever. The automatic update functionality of WordPress, for plugins and themes, never worked well. Occasionally it did, but usually I had to secure shell (ssh) and update manually.
I finally found the fix. Login to 1and1 using secure shell (ssh) . At the root of your account edit (vi) the .htaccess file. Add the following commands to the top:
AddHandler x-mapp-php5 .php AddType x-mapp-php5 .php
This applies to the 1and1 service.