intermittent problems using ftp_get ...Help!

Hi all Can anyone tell me what would cause intermittent problems downloading files using ftp_get. I have a php file that regularly connects to a number of servers in turn using php's (ftp functions) and downloads files using ftp_get(...). This usually works but often it just fails to download a file and ends up giving a timeout error. Also it seems it can be any file. I just cannot understand why when I run the script a number of times in sucsession this will sometimes but not others. Any ideas? p.s. The files I am downloading are '.sql' text files. Thanks K