I have managed to configure intergration between Office Web App server 2013 and Exchange 2013 OWA.
I have created a test users Test1 and Test 2. I have given full access on Test2 mailbox to user test 1.
When I login to owa for user test1 and preview the attachment it works fine.
However when I use "Open another mailbox" in OWA and open test2 mailbox and try to preview the attachments in test2 inbox it errors as " An error occurred while the document preview was being created. Please try again later " as follows