Urgent Indy Ftp Help Please

I am using indy v9 with delph v5 pro.

With the IdFtp.Put Command i set the append flag to true to appned a text
file to the internet ftp server.  This works fine on a Windows NT server but
on a Linux server I get a access denied error and cannot append a text file
on to the server

Please help !!

Regards

Lee