Configure Line:

'./configure' '--with-mysql=/usr/local/mysql' '--with-cybercash=/usr/www/www-utils/mck-3.3.1-i586-pc-linux-gnulibc2.1' '--prefix=/usr' '--exec-prefix=/usr' '--bindir=/usr/bin' '--sbindir=/usr/sbin' '--sysconfdir=/etc' '--datadir=/usr/share' '--includedir=/usr/include' '--libdir=/usr/lib' '--libexecdir=/usr/libexec' '--localstatedir=/var' '--sharedstatedir=/usr/com' '--mandir=/usr/share/man' '--infodir=/usr/share/info' '--prefix=/usr' '--with-config-file-path=/etc' '--enable-track-vars' '--enable-trans-sid' '--with-mysql=/usr' '--with-apxs=/usr/sbin/apxs' '--with-gd' '--with-freetype-dir=/usr' '--enable-gd-native-ttf' '--enable-gd-imgstrttf' '--with-jpeg-dir=/usr' '--with-png-dir=/usr' '--with-zlib' 

The Code:

    function CCEncrypt($message)
    {
        $session_key = sprintf("%s #%ld", date("D M j H:i:s Y"), getmypid());
        $enc_msg = cybercash_encr($this->merchant_key, $session_key, $message);
        $message = cybercash_base64_encode($enc_msg['outbuff']);
        $mac = cybercash_base64_encode($enc_msg['macbuff']);

        /* This adds the information needed to decrypt. */
        $encrypted_message = 'message=' . urlencode($message) . '&';
        $encrypted_message .= 'session-key=' . urlencode($session_key) . '&';
        $encrypted_message .= 'mac=' . urlencode($mac);
    
        return $encrypted_message;
    }


The Error:

Fatal error: Call to undefined function: cybercash_encr() in /usr/www/shanesworld.com/public_html/adm/class.cyberclass.inc on line 154

I have php 4.2.3 that I do a "make install" back and forth between this and 4.3.0rc1.  4.2.3 has no problem finding the function, and it is configured using the same ./configure line.

The code itself is part of CyberClass, which is available here:
http://www.zend.com/codex.php?id=115&single=1

I presume since I haven't had trouble with 4.2.3, it's something in 4.3.0.  Good luck ;)