apache error

[JOYDEEP]

Dear list,

I am running egw inside xampp for linux. in httpd.conf file I have

Listen 192.168.1.100:80

and appache doesn't hv any problem.

but when I modify the httpd.conf like

Listen 192.168.1.100:80
Listen 192.168.1.100:443

then appache reports

XAMPP: Error 1! Couldn't start Apache!
XAMPP: Starting diagnose...
XAMPP: Sorry, I've no idea what's going wrong.

could one kindly suggest my mistake ?
thanks