It's an issue with 1and1 and not having PHP 5 as the default install.
Adding the two lines to your .htaccess file will fix the problem. With the new lines in my .htaccess file I have no errors, without it the errors come back.
It is a very confusing problem with 1and1 as it acts as if it is a permissions issue but it's not.
For step by step...
The way I do it is to show hidden files in my FTP program (currently using Transmit on Mac). I then right click to edit my .htaccess file using what ever text editor I have available. Simply add the two lines:
AddType x-mapp-php5 .php
AddHandler x-mapp-php5 .php
I pasted them in the top of the file.
Save file and do a refresh of the overview page for the Gallery. It should now show you are using PHP Version 5.2.6 in the info area.
I have tested this tonight and without running PHP5 this plug-in and several others have issues on 1and1.
I have submitted a ticket to 1and1 about this, but adding the handler and type to the file works just fine.