Network error unable to reach the server when view contract with CiviHR
I have detected the issued.
I open apache log and saw the error 


  PHP Fatal error:  Call to undefined function file_upload_max_size() in /var/www/html/wordpress/wp-content/uploads/civicrm/ext/hrjobcontract/CRM/Hrjobcontract/Page/JobContractTab.php on line 46


So I go to the directory and edit that. Because the default value for max size when upload contract file is 10MB. So I change that. Every thing work well now.