How are you running the AEM instance?  As a run-as?  Sometimes AD/LDAP will request the credential from the contacting machine to validate network access.I also commonly use the ldp.exe tool from Microsoft to verify the connection before putting it in code.  Whatever details you work out with ldp.ex...

This used to be solved by creating the appropriate cross-domain.xml in the web-war descriptor files.There seems to be some header values you can set to allow the communication:https://developer.mozilla.org/en-US/docs/Web/HTTP/Access_control_CORS

What platform is it on, Windows or Linux?  Windows did you check the event log?  Linux did you check the /var/logs/messages.  I've seen instances shut down on Linux due to out of memory prevention.