I had similar problems when switching from a file based execution (setDataURL(...)) to a string based execution (setDataXML(...)). It turned out that I had special characters (e.g. %) in my string which, if loaded from file didn't cause any problems, but did when inputting the same XML as a string through setDataXML.
Once I removed all reserved characters from my XML string, the chart rendered fine even when initialized with na XML string instead of a file URL.