[10.04] FTP access through PHP(web) does not work...

[cholic]

I am in a VPS server which is in Ubuntu 10.04

I have installed PHP 5.3.2, Apache 2.2.4, VSFTPD, and some basic packages..
Users can use ftp to connect to the server and they can upload files if they want. Everything works as usual web hosting server.

However FTP access through PHP does not seem to work.
For example, Drupal has a feature which you can type in the url of the any tgz file (modules installation) to be downloaded on the server and installed automatically if I provide ftp information.

However, if I type in all correct information for ftp and click auto install, it says that I have typed in the wrong information. (which probably means it has failed)
Same thing happens for some other CMS, which uses ftp information typed in from user to download the file and install it automatically in the server.

In bash, if I just type in 'ftp' users gets connect to the server and it prints out ftp> shell.

Users, and apache2(run by user called 'www-data') are in same group called 'www-pub'
wget is also runnable by users and its group is set to 'www-pub'.

What do you think is the cause of problem?

[cholic]

By the way, listing directories using PHP functions ftp_connect, and ftp_nlist works...