Authentication failed. User is already authenticated as a different user

Hello,

I have downgraded our JVM to 1.4.2_13 and configure SPNEGO to accept Single Sign On. However now when I try to access the SAP Portal, it is giving me a blank screen. When I refresh the blank screen then it will give me the logon screen again. Here is the weird part, when I tried to log in with my network credential, it said "Authentication Failed: User is already authenticated as a different user." Does any one has an idea what is wrong? Before the SPNEGO implementation we were using LDAP and by using my network accounts I was able to log into the portal just fine.

Note: All network accounts are located on a separate AD domain then the SAP portal. The SAP portal domain and the network account domain had a trust set up between them.