Snapshot pro works on some but doesnt work on other servers

Hi there,

I was setting up Snapshot pro on all the websites I manage but I found a problem. It works fine on my DirectAdmin LAMP stacks, but does not work on my ServerPilot LAN(ginx)MP stacks.

I am trying to FTP the files to my back-up server. The test succeeds:

Using FTP connection
Connecting to host: x.x.x.x Port: 13321 Timeout: 5
Passive mode off.
Timeout set to 5
Login success.
Home/Root: /
Changing Directory: /backups/
Current Directory: /backups

The problem is that the files become 0 bytes on the remote server and the transfer fails:

2016-08-02 01:31:37: Sending Archive: 4.52M
2016-08-02 01:31:37: Destination: ftp: thuis
2016-08-02 01:31:43: Using FTP connection
2016-08-02 01:31:43: Connecting to host: x.x.x.x Port: 13321 Timeout: 5
2016-08-02 01:31:43: Passive mode on.
2016-08-02 01:31:43: Timeout set to 5
2016-08-02 01:31:43: Login success.
2016-08-02 01:31:43: Home/Root: /
2016-08-02 01:31:43: Changing Directory: /backups//
2016-08-02 01:31:43: Current Directory: /backups/
2016-08-02 01:31:43: ftp_put failed:
2016-08-02 01:31:43: ERROR: Only variables should be passed by reference

So I'm working with two different stacks. Everything works just fine on my other type of server.

How come it doesn't work on this type of stack?