setup php using omni https in pc

i have some problem in set up configuration using omni httpd. may i know why each time the setting that i type in External Tab and MIME tab became dissappear after i press the button add and ok and then came out from that tab?

In 'web server global settings' - external tab - in "virtual" type .php3 & in "actual" type chp3php.exe (or wherever yr version of PHP is located.

In the MIME tab -"actual" = wwwserver/stdcgi "virtual" = .php3 (yr version)

OMNI rejects typos and spelling mistakes as well as invalid paths.

Simon.

The setting that i chosen is obtain from the selection list provided by the tab in omni httpd and i also reading through the installation guide that downloaded from internet when i do this thing. i believe that it can't go wrong. can somebody explain and tell me the problem?