<?php

$url = 'http://www.php.net/';
$ch = curl_init($url);
if( !curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1))
{
        $error = curl_error($ch);
        $errno = curl_errno($ch);
        print("Could not set CURLOPT_RETURNTRANSFER (" . CURLOPT_RETURNTRANSFER .") because of error <$error> ($errno)\n");
}
else
{
        print("OK");
}
?>

Output:
$ ../cvs/php4/sapi/cli/php -f ../cvs/php4/test_curl.php
Could not set CURLOPT_RETURNTRANSFER (19913) because of error <> (136635288)

Config:
curl 7.9 (i386-pc-bsdi4.2) libcurl 7.9 (OpenSSL 0.9.6b) (ipv6 enabled)

#!/bin/sh

./configure \
        --prefix=/home/mdev/local \
        --enable-cli \
        --with-config-file-path=/home/mdev/local/etc \
        --disable-short-tags \
        --enable-pear \
        --disable-debug \
        --with-zlib-dir=/weblib/local \
        --with-openssl=/weblib/local \
        --with-mysql=/weblib/local \
        --enable-bcmath \
        --enable-calendar \
        --with-curl=/weblib/local \
        --with-mhash=/weblib/local \
        --with-pgsql=/pgsql \
        --enable-socket \
        --with-zip=/weblib/local \
        --enable-xslt \
        --with-xslt-sablot=/home/mdev/local \
        --with-expat-dir=/weblib/local \
        --with-sablot-js=/weblib/local \
        --with-iconv=/home/mdev/local \
        --enable-sysvsem \
        --enable-sysvshm \
        --enable-ftp

$ grep '\$Id:' ../cvs/php4/ext/curl/*.[ch]
../cvs/php4/ext/curl/curl.c:/* $Id: curl.c,v 1.115 2002/07/11 02:31:38 sniper Exp $ */
../cvs/php4/ext/curl/php_curl.h:/* $Id: php_curl.h,v 1.27 2001/12/11 15:28:58 sebastian Exp $ */