eXist-DB / XQuery - XSL transform unable to set up

Question

Environment: eXist-db 4.2.1 , XQuery 3.1, XSLT 2.0

I am firing off a transformation of an XML document in eXist-DB - XQuery which produces the following error:

exerr:ERROR Unable to set up transformer: no protocol: 
/db/apps/deheresi/styles/ms609__testxsl-withmodes.xsl [at line 265, column 26]

I haven't been able to locate this error in online documentation or searches. It's triggered by this XQuery:

declare function document:doc-xsl-docview($node as node(), 
  $model as map(*), $currentdoc as xs:string)

{   
  let $currentdocnode := doc(concat($globalvar:URIdb,$currentdoc))

  let $xi := concat("xinclude-path=", $globalvar:URIdb)

  let $xsltransform := transform:transform(
                        $currentdocnode, 
                        concat($globalvar:URIstyles,
                        "ms609__testxsl-withmodes.xsl"),
                        (<parameters>
                            <param name="paramPersonurl" value="{$globalvar:URLperson}"/>
                            <param name="paramPlaceurl" value="{$globalvar:URLplace}"/>
                            <param name="paramDocurl" value="{$globalvar:URLdoc}"/>
                         </parameters>),(),$xi)
   return $xsltransform
 };

All of the variables $globalvarare strings declared in a single module:

declare variable $globalvar:URIdb := '/db/apps/deheresi/';
declare variable $globalvar:URIdata := concat($globalvar:URIdb,'data/');
declare variable $globalvar:URImodules := concat($globalvar:URIdb,'modules/');
declare variable $globalvar:URIresources := concat($globalvar:URIdb,'resources/');
declare variable $globalvar:URIstyles := concat($globalvar:URIdb,'styles/');
declare variable $globalvar:URItemplates := concat($globalvar:URIdb,'templates/');

Thanks in advance...