Com error with DOM

I have a simple function to open an xml file and read a node value.
Every other time the function _XMLFileOpen() is encountered, I get "Com Error with DOM". This looks like a file close is not occuring, however, there is no file close function in the _XMLwrapper.au3

EG:
#include <_XMLDOMWrapper.au3>
#include <Array.au3>

$Node="StartTime"
$sXmlFile = "C:\Users\Mike\Documents\report.xml"
$sXPath = "//ReportInfo/prop[@name='" & $Node & "']"

_XMLFileOpen($sXmlFile)
If @error Then
MsgBox(0,"","error")
EndIf

$aRET = _XMLGetValue($sXPath)
_ArrayDisplay($aRET, "")

Even when encountering the error , the node value is still returned, obtained.
The error code is 0000000
If I exit my program, restart it, no error is encountered the first time
Any ideas????
Thanks