If you are using AttachView from Messageware you may receive this error – “OWA temporary unavailable”
after applying Exchange CU (Cumulative update) , and your users will unable to logon to OWA (IF the Mailbox of user is on the same server where you apply the CU).
Restart the IIS or the Server will not solve the Problem.
Download and Install the last Version Of AttachView from Messageware web site.
So Next time … you must verify that Messageware support the CU version that you want to Install on your Exchange Servers.