URGENT: Login screen appears in ESS

Dear Guru's,

We have a key user test very shortly and we just noticed that after an upgrade to SP 13 there is a strange thing in ESS in our Portal. We use FPN.

When we have logged in to our consumer Portal and navigate to the Employee Self Service scenario (Remote Role from our Producer Portal) and click on a certain Webdynpro, we get redirected to the Portal login page! How ever, when we click 'ok' without filling in any username or password we proceed correctly to the correct application.

I am under the impression that this resides in some kind of cookie or ticket problem, but I can't find the cause. Please help me on short notice. Any help will be highly appreciated and will be rewarded with SDN Points!

Thanks in advance and best regards,

Jan Laros