Forms Builder Error

I'm building a form in Form Builder that load data from a mysql database to a select control when the form starts. When I test the form the form runner says "Content is not allowed in prolog". I think that is in the expression

<xforms:insert nodeset="instance('fr-service-request-instance')"
                                   origin="saxon:parse(instance($request-instance-name))"/>

I replace saxon:parse(instance($request-instance-name)) for instance($request-instance-name) and the forms doesn't get any data. How can I make a database service in Form Builder? I need to initialize a select (drop down) with data from a table in MySql. Any help?

Thanks