WoltLab Installation Error

Why do I get this when I try to install WoltLab?:

Fatal error: There is no access to the system temporary folder due to an unknown reason and no user specific temporary folder exists in /membri/juarezcorp/! This is a misconfiguration of your webserver software! Please create a folder called /membri/juarezcorp/tmp/ using your favourite ftp program, make it writable and then retry this installation.

You get more information about the problem in our knowledge base: http://www.woltlab.com/help/?code=10000
Information:

error message: There is no access to the system temporary folder due to an unknown reason and no user specific temporary folder exists in /membri/juarezcorp/! This is a misconfiguration of your webserver software! Please create a folder called /membri/juarezcorp/tmp/ using your favourite ftp program, make it writable and then retry this installation.
error code: 10000
file: /membri/juarezcorp/install.php (267)
php version: 5.2.17
wcf version:
date: Tue, 29 May 2012 02:32:26 +0000
request: /install.php
referer: http://s137.altervista.org/lf.pl?sid...1125d21b8d4e41
Stacktrace:

#0 /membri/juarezcorp/install.php(701): BasicFileUtil::getTempFolder()
#1 {main}


Can someone please help me?

Nevermind... I just found out =D