EWS API Retuning Login page as Reponse - Exchange Server 2010

Question

Hi!
I'm currently working with the EWS API to pull calendars and events from an Exchange Account.  I'm using the Microsoft.Exchange.WebService.dll v15.
My code works fine for an Office 365 hosted account.  But for Exchange Server 2010, I get the error:
The response received from the service did not contain valid XML.
After enabling tracing, I've learned that the response is actually the login page, not the expected XML with the calendars.  It's returning the HTML of the login page as the response.
At this point, I'm unsure of what's going on.  Any help is greatly appreciated.  In the meanwhile, I'll keep poking around.
Thank you!

Answer 1

The place to start would be to check your EWS End Point 
how are you getting this ?
Are you use Autodiscover ?
Do they have a different Internal vs External EWSUrl ? where are you running your code from ?
If your getting a Logon prompt it sounds like FBA has been enabled on the EWS directory or is it being published through a reverse Proxy ?
You should be able to just use a browser against the endpoint to test it you might want also want to use the EWSEditor
http://ewseditor.codeplex.com/ to try to do some testing against different endpoints (eg try just use the Cas ServerName and building to the URL yourself instead of using Autodiscover eg
https://casservername/ews/exchange.asmx ) 
You can also do some external testing using
https://testconnectivity.microsoft.com/
Cheers
Glen