OWA Displays Unexpected Error
OWA experinces an unexpected error when you try to browse and your request couldn’t be handled
In Exchange 2010, 2013 you might get an error in OWA when trying to access calendar.
Cause and Resolution 1:
This error could happen to you if you set a redirection of OWA has been configured. To fix the issue simply remove the redirect option.
Another resolution that works without turning Redirection off for default site is to turn off redirection from the Public folder.