I'm trying to install ajaxplorer at a shared hosting in my home folder. When I navigate to the main page, I get an error:

is_writable(): open_basedir restriction in effect. 
    File(/var/lib/php5) is not within the allowed path(s): 
    (/var/www//username/:/usr/sbin/sendmail:/usr/share/php
        :/home/www/appname::/usr/share/pear:/dev/urandom)

What might be the cause? How could I fix it?

There is php 5.3.3 installed, apache 2.2.16. I use ajaxplorer 4.0.4.

EDIT:

The problem is caused by this code part:

$tmpDir = session_save_path();
$this->testedParams["Session Save Path"] = $tmpDir;
if($tmpDir != ""){
   $this->testedParams["Session Save Path Writeable"] = is_writable($tmpDir);

Error appears in the last line, but I enclosed the context.