Has anyone gotten SSO to work with web access and SAP Netweaver? The initial reply is is a www-negotiate then after kerberos ticket is created and forwarded it sends the user to a form logon page. A web post directly to the form doesn't seem to work .
I have come across this situation and I have also see it working through Kerberos Authentication.
When you say that the kerberos ticket is created and then it is forwarded to Form Based, I suspect the kerberos authentication to be failing. So, it is failing over to Form Based.
Please check the Kerberos SSO configuration. (User access log and TCP dump should give you an insight of what is happening)