Fix an iPad app (reposted final)

I have an ipad app that retrieve datas from an ftp server. Connecting by using login and pass, it retrieves the list of files and directories, and clicking on one of these items it downloads it (also, it's admitted to download all files from that ftp by simply clicking a button). The fact is that this app doesnt work very well and sometimes when I try to download a file it's not succesfull like it seems it lost connection with the ftp (before this ftp server we used and http server and everything was working correctly, also with the http connection i was able to display a progress bar of the download but with this ipad i had to delete it). I need to understand why this happen (could be a problem of ftp server that has worst performances of http?) and fix it. Of course I have xcode source files.