JDeveloper, Java & XML :: Process XML Data Passed In Parameter

I have a requirement to extract data from an XML formatted string that is passed as an IN parameter to a database stored procedure. I do not have a table to store the XML, nor an XML schema, nor a namespace, just the XML string. While new to XML, I do understand the basics. Using XMLTable I am able to parse out the simplest of XML data. My problem is this; attempting to extract data from nested XML nodes results in the error

'ORA-19279: XQuery dynamic type mismatch: expected singleton sequence - got multi-item sequence'.

Testing a solution example I found on this site by Barbara Boehmer, I still get the ORA-19279 error. I suspect it may be because I have version 10g while she has version 11g. Her solutions is from #msg_514154. Here is that code that gives me the error:

SCOTT@orcl_11gR2> SELECT x."deptno"
2 FROM (SELECT '<departments><deptno>1</deptno><deptno>2</deptno></departments>' col FROM dual) xml_data,
3 XMLTABLE
4 ('/departments/deptno'
5 PASSING XMLTYPE (xml_data.col)
6 COLUMNS
7 "deptno" number path '/deptno') x
8 /

deptno
----------
1
2

2 rows selected.

As I said, this example generates the ORA-19279 error. Need processing XML data from an IN parameter?