All of a sudden our API (soap) stopped working for a DF19.0 webapplication with the below error. Nothing in the Event log.
Checked all other SAXParseException errors I found on the forum, but to no avail.

HTML Code:
Application error occurred during processing.Technical details for the site administrator: 
Internal error: SAXParseException: invalid document structure (Occurred in an unknown entity, at line 1, column 1.) 
Please check the Windows event log for further information about the problem.
Any ideas? :-)