OWA problem

Hi,

I have a problem on OWA ,when i open archived item it says that;

" The archived item is currently unavailable. If you choose reply or forward, only the content shown below will be included. Click here to preview the original item."

When i click the information, it asks the password and if i enter correct credentials archived mail opens.

why it couldnt open directly and it needs credentials in every mail?

exch 2010 sp2 , owa 2010

ev 9.03

thanks...