I installed OmniHTTPD 2.0 and PHP4 with steps.
d:\HTTPD\
d:\HTTPD\PHP-BIN
C:\WINDOWS\php.ini , .dll files.
D:\HTTPD\PHP4\PHP.exe , .ini and .dll files.
I got the error given in title.
What I changed in my php.ini file is:

doc_root		= d:\HTTPD\HTDOCS

;Windows Extensions
;extension=php_mysql.dll
extension=php_nsmail.dll
extension=php_calendar.dll
extension=php_dbase.dll
;extension=php_filepro.dll
;extension=php_gd.dll
;extension=php_dbm.dll
;extension=php_mssql.dll
;extension=php_zlib.dll
;extension=php_filepro.dll
;extension=php_imap4r2.dll
;extension=php_ldap.dll
;extension=php_crypt.dll
;extension=php_msql2.dll
;extension=php_odbc.dll

sendmail_from	=	elanor@universalmail.com

The rest of the php.ini file are the same with default.

I added .php both MIME and EXTERNAL in OmniHTTPD

When I try to run a script, it gives
Standard CGI Launch Error and Windows Error Message given in title.

Did I do something wrong, or this is because of missing step!