apache web server can't start

[louiseXampp]

I installed Xampp5.6.33-0 on mac os 10.10.3. control panel is XAMP 5.6.33-0

1. I started apache web server in the Manager Servers page.
2. in the Application log, it shows that the process started. But, the red light is on. http://localhost shows "It works". what is going on ?

Starting Apache Web Server...
/Applications/XAMPP/xamppfiles/apache2/scripts/ctl.sh : httpd started
Starting MySQL Database...
/Applications/XAMPP/xamppfiles/mysql/scripts/ctl.sh : mysql started at port 3306
Starting ProFTPD...
Checking syntax of configuration file
/Applications/XAMPP/xamppfiles/proftpd/scripts/ctl.sh : proftpd started
Starting Apache Web Server...
/Applications/XAMPP/xamppfiles/apache2/scripts/ctl.sh : httpd started
Starting Apache Web Server...
/Applications/XAMPP/xamppfiles/apache2/scripts/ctl.sh : httpd started
Starting Apache Web Server...
/Applications/XAMPP/xamppfiles/apache2/scripts/ctl.sh : httpd started