ECONNREFUSED - Connection refused by server PROFTPD

Question

I have a problem with my server. I installed proftpd in my server, and on filezilla its work. But sometime i have this following error

ECONNREFUSED - Connection refused by server

So, i have to go on my server and restart my proftpd with this following code:

sudo /etc/init.d/proftpd restart
 * Stopping ftp server proftpd                                           [ OK ]
 * Starting ftp server proftpd                                           [ OK ]

Then its work again.

The problem is that i have this error every week so i have to restart each time.

Thanks for your help.