are you getting this message when the ini is extracting from your datasource and creating the xml file or when the import mapping is happening? If it is during the import mapping process then I would check how you have set up that mapping. That is where you set the primary keys, etc.
The problem was solved. What I did was to change the xls headers, ini and import mapping to upper case. And the "Reference to" field is needed otherwise triggers the next error: JDBC error: msg=ORA-01722: invalid number.