Enctype issue when I try to upload a file with a Coldfusion webservice

Can't get to work a Coldfusion webservice that uploads a file in an external server.

My application runs in "Server A" and the file repository (external server) is in "Server B"

The template (inicio.cfm) which contains the form with the <cfinput type="file"> to select the client's file to be uploaded, is stored in "Server A". This template performs more tasks than just show the upload form. It performs calculations, queries, etc. outside the form's code block. Also, the action page of this form is the template itself (because of my application's needed tasks).

The first code line of my form definition is (inside inicio.cfm):

<cfform method="post" name="AltaConvocatoria" enctype="multipart/form-data">

Which demonstrate that I'm using the right enctype definition.

In the other hand, stored in "Server B" is my Coldfusion component or webservice (alta_ga.cfc) which only task is to upload the file selected by user in "inicio.cfm" form and rename it.

Here's alta_ga.cfc code:

<cfcomponent>

    <cffunction access="remote" returntype="void" name="cargaAnuncio">

        <cfargument name="destinoAnuncio" required="yes" type="string">

        <cfargument name="PrefijoNvoNombre" required="yes" type="string">

        <cffile action="upload"
        fileField="str_ArchivoAnuncio"
        destination="#destinoAnuncio#"
        nameconflict="Overwrite">
        <cfset NvoNomAnuncio = #PrefijoNvoNombre# & #Right(cffile.ClientFile, 5)#>

        <cfset viejoNombre1 = #destinoAnuncio# & #cffile.ClientFile#>

        <cffile
        action = "rename"
        destination = "#NvoNomAnuncio#"
        source = "#viejoNombre1#">

    </cffunction>

</cfcomponent>

For that pupose, I invoke the webservice from the form's action code block in inicio.cfm with this:

<cfinvoke webservice="http://192.168.208.128/podi/mgmt/alta_ga.cfc?wsdl" method="cargaAnuncio" >
    <cfinvokeargument name="destinoAnuncio" value="#form.destinoAnuncio#" />
    <cfinvokeargument name="PrefijoNvoNombre" value="#form.PrefijoNvoNombre#" />
</cfinvoke>

When I try to load a file using my form's template inicio.cfm I get this message:

Cannot perform web service invocation cargaAnuncio. The fault returned when invoking the web service operation is: '' podi.mgmt.PodiMgmtAlta_gaCfcCFCInvocationExceptionException: coldfusion.tagext.io.FileUtils$CFFileNonMultipartException : Invalid content type: application/soap+xml; charset=UTF-8; action="urn:cargaAnuncio".The files upload action requires forms to use enctype="multipart/form-data".]

All the arguments and variables that I'm using are correct, because I tested the webservice as a local component (stored in Server A and uploading the file in the same server) and worked fine. Here's the code of the succesful test (invoked as a component instead of a webservice):

<cfinvoke component="alta_ga" method="cargaAnuncio" destinoAnuncio="#form.destinoAnuncio#" PrefijoNvoNombre="#form.PrefijoNvoNombre#">

¿What could be wrong? There's a lack of documentation about this functionality. Adobe's user guide doesn't explain this functionality in depht. Ben Forta's books... same. Or I couldn't find the information. Thanks in advance.