In some cases, due to improper login to at the onset, user may have issues with opening attachments in OWA
a faster way to resolve this is by using adsiedit
while in ADSI, go to properties of user and set this attribute MSExchMailboxFolderSet to 2147483647
This setting enables all OWA features.
Note: In some cases, user still has his/her outlook web access frozen and not able to do anything.
re-creating user’s profile on the workstation fixed the problem