You need to talk to your web host Versio.nl; something is amiss with their shared server configurations.
Files and folders should never be 777. WordPress needs no more than 644 on files and 755 on folders. And WordPress should be able to create directories.
Some plugins require the /wp-content/ folder be made writeable, but in
such cases they will let you know during installation. In some cases,
this may require assigning 755 permissions.
From http://codex.wordpress.org/Changing_File_Permissions :
Typically, all files should be owned by your user (ftp) account on
your web server, and should be writable by that account. On shared
hosts, files should never be owned by the webserver process itself
(sometimes this is www, or apache, or nobody user).Any file that needs write access from WordPress should be owned or
group-owned by the user account used by the WordPress (which may be
different than the server account). For example, you may have a user
account that lets you FTP files back and forth to your server, but
your server itself may run using a separate user, in a separate
usergroup, such as dhapache or nobody. If WordPress is running as the
FTP account, that account needs to have write access, i.e., be the
owner of the files, or belong to a group that has write access. In the
latter case, that would mean permissions are set more permissively
than default (for example, 775 rather than 755 for folders, and 664
instead of 644).