I have kind of a weird situation. At one point I enabled ECP externally and it was working fine (though I had considered removing it for security reasons). Over this past weekend I applied Exchange 2013 CU4/SP1. That is the only change I can put my finger on. As of today when I attempt to access my ECP internally I am presented with the logon page as usual; after providing my credentials I get:
This error (HTTP 400 Bad Request) means that Internet Explorer was able to connect to the web server, but the webpage could not be found because of a problem with the address.
Oddly, I can access ECP externally just fine. Likewise, OWA works fine inside and out, as does EAS.
I've removed and re-created the OWA virtual directory then re-created it, resetting IIS afterward. I've checked all the settings in the virtual directories and IIS but am clearly missing something. Thank you in advance for any ideas any of you may have.