webdynpro application page builder expired error

Hi Guru's

    I am implementing portal through the apache reverse proxy. There are some custom developed webdynpro application in the portal. The webdynpro applications or iViews works fine if i access the portal directly (http://<portalserver:port>/irj), but if come through the reverse proxy and access the webdynpro iview in portal, i get the following error

'The webdynpro application 'Page Builder' has expired'.

I am using NW04s Portal (EP7.0). I desperately need all of your help. We are going live in a weeks time.

Tommy