ACL code not working

Using acl scripting in Arbortext Editor 6, How can an sgml file be opened and then save it as xml?

The doc_open method below returns a document identifier.

Providing this document identifier to the doc_save function saves an empty xml file.

Sample ACL Code:

#Open a sgml file

#0x200 - Open the document without loading a stylesheet.

$sgml_doc = doc_open("file.sgml", 0x200)

#save as xml

#0x0020 - Write the document as an XML document

doc_save($sgml_doc, 0x0020, "file.xml")

What should be done differently?