Hi Borut,
To troubleshooting the issue, please install Update Rollup 1 for AD FS 2.0 on all AD FS 2.0 on all AD FS 2.0 Federation Service farm nodes. For more info about how to download and install Update Rollup 1 for AD FS 2.0, please click on the link below.
http://support.microsoft.com/kb/2607496
This update requires a restart of the computer. Please let me know whether the issue still exists after performing this activity.
Thanks,
Yang Yu
