SSO Kerberos and IE7

Hey Experts,

I have problem with SSO Kerberos, and IE 7,

If I use the short url http://servername:50000/irj/portal, SSO is working but if I use the long URL http://servername.corp.company.org:50000/irj/portal SSO is not working and I'll get the NTLM prompt

but I can use both URL in IE 6 without any problem.

I try in EP7 SP15 and EP6 SP17

any idea?

Thanks