Issues:

1. Remove the exppw.dll entry from applicationhost.cofig (c:\windows\system32\inetsrv\config)Note: Remember take a backup before you remove the line.
2. Then registered the exppw.dll by following the below steps:

1. IIS Manager -> Select the Server Name in the left Pane -> Open Modules in the middle pane.
2. Click on ‘Configure Native Modules’ in the right pane -> Click the button ‘Register’ -> Type the name as ‘exppw’
3. Browse and select the path of above file as: c:\Programme Files\Microsoft\Exchange Server\V14\Client Access\OWA\Auth\exppw.dll.
4. Made sure that the ‘exppw.dll’ is only present at OWA level and not at any of the top heirarchy.
5. Then ensured for this module in OWA (VDir), ‘Module Type’ is set to ‘Native’ and ‘Entry Type’ is ‘Local’
6. Run IISreset /noforce