Http://localhost/nagios/ download a file!

Why when I try to acces the nagios web interface via browser localhost/nagios it downloads a file (4kb without extension) instead of accesing to the interface???

The first time, a prompt for a username and password, but also a file downloaded.

I’ve tried with:

#/opt/nagios/plugins/check_http -H 127.0.0.1

#/opt/nagios/plugins/check_http -H 127.0.0.1 -u /nagios/ -a nagiosadmin:

and different options like /nagios/cgi-bin/tac.cgi and it works!! the answers are right:

HTTP OK: HTTP/1.1 200 OK …

What happens?? why is it downloading a file instead of accesing the interface???

Thanks a lot for the help, I need it.

Are you sure you installed apache and PHP correctly?