FTP in WordPress on Ubuntu 11.04

I have recently installed WordPress on my Ubuntu Server machine. I have had constant problems with the FTP that WordPress uses. I have set up the FTP server properly, as far as FileZilla and every other client in the world is concerned. But as soon as I try to use the wp-admin version of FTP, it claims it cannot find the directory. I use proftpd for the server on my machine. I have set up passive FTP properly, and allow external connections.

Any help at all will be greatly appreciated.