$this->ftp->mkdir not working

[eluser]Unknown[/eluser]
Hello,

i am trying to make a new folder.
In my script, when a new user creates an account, a new folder should be
placed on the server....

but nothing happens:

Code:

$this->load->library('ftp');
$this->ftp->mkdir('uploads/new_folder/');

There is NO error message....

I don´t know what to do...It is perhaps a problem with chmod ?
Should i set the "parent directory" (here 'uploads') to chmod 777 ?

Any ideas,

Greetings,
Julian