You don't have the necessary rights to execute that file. If the server you're running the script has linux use the chmod command to change file permissions.
chmod 0764 /var/www/html/example/src/frapi/custom/Action/BackgroundTask/log_file.log
4 = read;
2 = write;
1 = execute;
read+write+execute = 4+2+1 = 7;
764 means rwx for owner, rx for group, r for others.
For further documentation please refer to: https://help.ubuntu.com/community/FilePermissions