Unable to change Data Source for NW04S Preview

Greetings-

I have changed all settings in the ConfigTool to authenticate against our Active Directory. However, we use a custom attribute to store SAP ID, so I need a custom XML file in the UME. Whenever I try to upload a file, I receive a "File is not a valid configuration file" error. I am not even able to upload the supplied file back into the portal without the same error. Can anyone help?