From Baan Support Site
This is what I saw on the Baan support site. I'm not sure if it is related to your problem but perhaps it is of any help
Important Note for iBaan Portal Users:
We inform you that the latest version of TopTier Portal (iBaan Portal 4.5) is incompatible with Internet Explorer 6.x he current certified version is IE 5.5 or earlier. Version 4.5 of iBaan Portal does not work consistently with Internet Explorer 6.0 and there are issues with reverting IE 6.0 back to IE 5.5. Hence please do not load iBaanPortal 4.5 onto a machine that is running IE 6.x.
This limitation is also briefly documented in the User Manual, U7661A US - User's guide for iBaan Portal Version 4.5 Running on MS Internet Explorer
(Software requirements page 2-2):
We are currently working to resolve the compatibility problems, and do not have a release date yet.