Plesk 12.x / Linux :: Removing FTP-user Through API Results In 500 Internal Server Error (PHP)

To automate some tasks for some projects I'm working on, I need to be able to automatically create or delete ftp-users.

Creating and listing ftp-accounts is working great, but when it comes to deleting them I run into an internal server error. Before my script gets the response it's waiting for, the script crashes.

- When live watching the Apache error-log with 'tail -f', the terminal-session is exited with 'Killed (core dumped)'
- Apache error-log shows:

Code:
(104)Connection reset by peer: mod_fcgid: error reading data from FastCGI server, referer: http://example.com/ftp.php?action=delete
Premature end of script headers: ftp.php, referer: http://example.com/ftp.php?action=delete
- Webbrowser shows default '500 Internal Server Error'

I have checked and changed time-out settings, but it didn't work. Error occurs a few seconds after executing, while the timeouts are set to 60 to 90 seconds.

Packet send to Plesk:

Code:
<?xml version="1.0" encoding="UTF-8"?>
<packet version="1.6.6.0">
<ftp-user>

[Code].....