OWA not working and showing red Xs instead of the images?
it is possible for the IUSR anonymous auth account password to get out of sync between where its held in AD and the metabase
you can test this by unchecking anonymous auth on default website and exchweb and enabling IWA
stop and start the default website
does IWA auth work with OWA?
if so the password for anonymous auth are out of sync
https://support.microsoft.com/kb/297989 helps getting them back in sync