FTP fopen() error 550—not a plain file - php

Question

Well, this is a problem I have never seen before.
I am trying to stream an FTP file using PHP's fopen() and feof() in order to copy it from one server to my own. This works fine when using normal http:// URLs. However, when using the ftp:// protocol, I'm receiving the following error:
fopen(ftp://.../streaming/planted2.mp4) [0function.fopen0]: failed to open stream: FTP server reports 550 /streaming/planted2.mp4: not a plain file.
Bear in mind that I have confirmed the URL is correct.
If I pop it into my browser's search bar, it always loads correctly.
Following this error, any attempt to use feof() or fread() on the wrapper results in an error complaining that the respective function expects a resource, but that instead a boolean is being provided. This would not be the case if fopen() was not failing.
As the files are quite large (several gigabytes at times) streaming is mandatory. Also, due to the configuration of the server, I need a way to loop through each chunk in order to buffer some output. If I don't, the server holds up. It's a weird configuration on Rackspace's behalf. That's why I'm using feof().
So, without further ado, my question is this: What does the 550 error mean, and what is a "plain file"? If it is a problem with the configuration of the server I am attempting to download from, what are my options, given my limitations?
EDIT
I have determined this is a server issue. However, the problem is still unresolved.
I contacted my boss and our server administrator, and the server guy told me to test this out on a different Windows-based server instead of the Linux-based one I was playing with. My script works with the Windows server, so I have confirmed my script is not in error.
Unfortunately, my boss still wants me to figure out the problem, and find out why it's not working on the Linux box. I have absolutely no idea why, and don't know where to look. Any hints would be greatly appreciated!

Answer 1

I've just come across this issue when trying to get a file from a sco unix server.
Server File Location: /home/user/data/myfile.csv
I can put the below into any browser and it gets the file.
ftp://user:password#host/data/myfile.csv
However if I run the below, I get the same error as you
$f = fopen("ftp://user:password#host/data/myfile.csv", "r");
However, if I put the full path into fopen - it works fine.
$f = fopen("ftp://user:password#host/home/user/data/myfile.csv", "r");
I'm not sure if this will fix it for you, but works for me.