I get this error whenever I try to import a feed into the website. The vps I got is this:

Server Host: centos (91.92.109.48)

Server OS: Linux 2.6.32-042stab108.2

Server Date: 06/01/2016 09:45:58

Server Up Time: Unsupported

HTTP Server: Apache/2.2.31 (Unix)

PHP Version: 5.6.20 (Zend: 2.6.0)

PHP File Uploads: On

Upload Max Size: 128M

PHP Memory Limit: 1024M

POST Max Size: 128M

Database: MySQL 5.5.49

Database Host: 127.0.0.1 (127.0.0.1)

Database Date: 06/01/2016 09:45:58

Database Data Size: 457 kB

Database Index Size: 464 kB

MySQL Slow Query Log Status: On

MySQL Slow Query Log File: /var/lib/mysql/centos-slow.log

MySQL Mode: (None set)

and zen cart 1.5.5

[31-May-2016 17:22:11 UTC] Request URI: /zcadmin/configuration.php?gID=31&cID=547&action=edit, IP address: 172.93.102.178
#1 call_user_func() called at [/home/soft/public_html/XXXXXXXXXXX.com/zcadmin/includes/functions/general.php:1800]
#2 zen_call_function() called at [/home/soft/public_html/XXXXXXXXXXX.com/zcadmin/configuration.php:129]

[31-May-2016 17:22:11 UTC] PHP Warning: call_user_func() expects parameter 1 to be a valid callback, function 'zen_cfg_select_option(array('true', 'false'),' not found or invalid function name in /home/soft/public_html/XXXXXXXXXXX.com/zcadmin/includes/functions/general.php on line 1800
[31-May-2016 17:22:11 UTC] Request URI: /zcadmin/configuration.php?gID=31&cID=547&action=edit, IP address: 172.93.102.178
#1 call_user_func() called at [/home/soft/public_html/XXXXXXXXXXX.com/zcadmin/includes/functions/general.php:1800]
#2 zen_call_function() called at [/home/soft/public_html/XXXXXXXXXXX.com/zcadmin/configuration.php:129]

[31-May-2016 17:22:11 UTC] PHP Warning: call_user_func() expects parameter 1 to be a valid callback, function 'zen_cfg_select_option(array('true', 'false'),' not found or invalid function name in /home/soft/public_html/XXXXXXXXXXX.com/zcadmin/includes/functions/general.php on line 1800