reset cas-mailbox for a user

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
 
Resolution:
 
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