Calling Reporting Services Render using Soap Envelope

I'm having a lot of trouble achieving a simple alteration to some code which previously worked on Reporting Server 2000, but now needs to work on Reporting Services 2008R2. I'm trying to avoid redeveloping the whole solution, and would just like to unlock the problem with this code. I'm currently getting an error:

<faultstring>The value for parameter 'Format' is not specified. It is either missing from the function call, or it is set to null. ---> Microsoft.ReportingServices.Diagnostics.Utilities.MissingParameterException: The value for parameter 'Format' is not specified. It is either missing from the function call, or it is set to null.</faultstring>

This is from the ResponseText returned after the line

oXMLHTTPRequest.send (oDocument.XML)

The function code is below. I'm setting the Format property as "PDF" and I can't see why that'd be a problem. Do I have a namespace wrong, a case-sensitivity issue, or is this form of calling the Render method not supported in 2008R2?

Public Function GenerateReportingService(oDom As MSXML2.DOMDocument, sReportName As String) As Variant
Dim sSOAPMsg As String
Dim oDocument As New MSXML2.DOMDocument60
Dim oXMLHTTPRequest As New MSXML2.XMLHTTP60
Dim sParamName As String
Dim sParamValue As String
Dim sUserName As String
Dim sPassword As String
Dim sWebMethod As String
Dim sReport As String
Dim sFormat As String
Dim sHistoryID As String
Dim sDeviceInfo As String
Dim sShowHideToggle As String
Dim sWebservicesURL As String
Dim sWebservicesURI As String
Dim nodeReport_Line As MSXML2.IXMLDOMNodeList
Dim nodeInvReport_Line As MSXML2.IXMLDOMNodeList
Dim nodeXMLErrorMsg As MSXML2.IXMLDOMNodeList

sWebservicesURL = Reg_ReadRegistry(HKEY_LOCAL_MACHINE, REGKEY_REPORTS, REGKEY_REPORT_PATH) 'http://sqlrs01/reportserver/reportexecution2005.asmx/
sWebservicesURI = "http://schemas.microsoft.com/sqlserver/2005/06/30/reporting/reportingservices/"
sReportName = Trim(sReportName)

Select Case sReportName
	Case "XML_ELEMENT_BR01_INVENTORY_ROOT"
		sReport = "/Binstock Reports/InventoryReport"
		sParamName = "XmlString"
	Case "XML_ELEMENT_BR02_ADJUSTMENT_ROOT"
		sReport = "/Binstock Reports/AdjustmentReport"
		sParamName = "XMLString"
	Case "XML_ELEMENT_BR03_STOCK_COUNT_ROOT"
		sReport = "/Binstock Reports/StockcountReport"
		sParamName = "XMLString"
End Select

sFormat = "PDF"
sDeviceInfo = vbNullString
sShowHideToggle = vbNullString
sWebMethod = "Render"
sParamValue = oDom.XML
Set nodeReport_Line = oDom.getElementsByTagName("report_line")
Set nodeXMLErrorMsg = oDom.getElementsByTagName("error_level")
Set nodeInvReport_Line = oDom.getElementsByTagName("report_line")

If (nodeReport_Line.length = 1) Then
	If (nodeXMLErrorMsg.Item(0).Text = "0") Then
		sParamValue = Replace(sParamValue, "<message>", "<message>.")
		sParamValue = Replace(sParamValue, "<MESSAGE>", "<MESSAGE>.")
	End If
End If

sParamValue = Replace(sParamValue, vbCrLf, "")
sParamValue = Replace(sParamValue, "<", "&lt;")
sParamValue = Replace(sParamValue, ">", "&gt;")

sSOAPMsg = "<?xml version='1.0' encoding='utf-8'?>" & vbCrLf
sSOAPMsg = sSOAPMsg & "<soap:Envelope xmlns:soap = 'http://schemas.xmlsoap.org/soap/envelope/' xmlns:xsi = 'http://www.w3.org/2001/XMLSchema-instance' xmlns:xsd='http://www.w3.org/2001/XMLSchema'>"
sSOAPMsg = sSOAPMsg & "<soap:Body><Render xmlns = 'http://schemas.microsoft.com/sqlserver/2005/06/30/reporting/reportingservices/'>"
sSOAPMsg = sSOAPMsg & "<Report>" & sReport & "</Report>"
sSOAPMsg = sSOAPMsg & "<Format>" & sFormat & "</Format>"
sSOAPMsg = sSOAPMsg & "<DeviceInfo>" & sDeviceInfo & "</DeviceInfo>"
sSOAPMsg = sSOAPMsg & "<Parameters><ParameterValue><Name>" & sParamName & "</Name><Value>" & sParamValue & "</Value></ParameterValue></Parameters>"
sSOAPMsg = sSOAPMsg & "<Credentials><UserName>" & sUserName & "</UserName><Password>" & sPassword & "</Password></Credentials>"
sSOAPMsg = sSOAPMsg & "<ShowHideToggle>" & sShowHideToggle & "</ShowHideToggle>"
sSOAPMsg = sSOAPMsg & "</Render></soap:Body></soap:Envelope>"

oDocument.loadXML sSOAPMsg

oXMLHTTPRequest.open "POST", sWebservicesURL, False
oXMLHTTPRequest.setRequestHeader "Accept", "text/xml"
oXMLHTTPRequest.setRequestHeader "Cache-Control", "no-cache"
oXMLHTTPRequest.setRequestHeader "SOAPAction", sWebservicesURI & sWebMethod
oXMLHTTPRequest.setRequestHeader "Content-Type", "text/xml; charset=utf-8"
oXMLHTTPRequest.send (oDocument.XML)

GenerateReportingService = SavePDF(oXMLHTTPRequest.responseText, COMPONENT_NAME, sReportName)
End Function

I've done extensive searching for a solution to this and am really struggling.

Thank you.

Tim Johnstone Senior Technical Consultant Computacenter (UK) Ltd