I spent so much time debugging this, most sites don't tell you a very important option to use with CURL and you will only find out this is the problem by running the PHP script from the command line you get the following output that shows the issue (I don't see any way to get this output from Apache itself).
* About to connect() to ip.ip.ip.ip port 25000
* Trying ip.ip.ip.ip... * connected
* Connected to ip.ip.ip.ip (ip.ip.ip.ip) port 25000
This is a great way to use your ftp server space, for example on your web hosting account (althoughI believe many hosts don't allow storage like this), but if you have a VPS/Dedicated Server etc.., this would be perfect. Imagine how easy it is to work with an ftp account that you can just mount as a normal partition or directory in Linux, it would be great for backups etc..
curlftpfs - mount a ftp host as a local directory