Java Security

I've added logic to my application to use certificates. When I logon, I am asked for a certificate, I select one and then continue on to my application.

The logic uses this code I got from someone else on the project.

weblogic.security.X509 certChain [] =
(weblogic.security.X509 []) request.getAttribute("javax.net.ssl.peer_certificates" );

ByteArrayOutputStream bos;
ByteArrayInputStream bis = null;

CertificateFactory certFactory = CertificateFactory.getInstance("X.509");

try {
bos = new ByteArrayOutputStream();
certChain[0].output(bos);

bis = new ByteArrayInputStream(bos.toByteArray());

myCertificate = (X509Certificate)certFactory.generateCertificate(bis);

extractCertificateSubject(myCertificate);

} catch (IOException e) {
throw new CertificateException();
}


The first time this code executes, the CertificateFactory.getInstance("X.509") works fine.

After I logoff and try to logon again, (whether or not I close my browser first), I am not prompted for a certificate but instead get this exception:

java.security.cert.CertificateException: X.509 not found
at java.security.cert.CertificateFactory.getInstance(CertificateFactory.
java:176)

What would cause this exception to occur even though I have successfully executed the getInstance before?

I am running WebLogic 5.1