writing to file on server

Hi, I've just started working with PHP. I've made a guest book using PHP (nothing spectacular) that worked just fine when I tested it op my pc, but when I uploaded it, it stopped working. My specific problem is that I cannot write to a file that already exists and contains data. When I try to I get these warnings: Warning: File already exists Warning: fopen("ftp://...@ftp.myhost.com/guestbook.txt","a") - File exists Is this problem related to the FTP fopen? And is there a way to correct this problem? Tnx! Joeri Vankelst