Mistyping

[phongvants123]

xpath='/CHandlingDataMgr/HandlingData/Item[@type="CHandlingData"]/handlingName[.="BUFFALO"]/../fMass'>

It should be

xpath="/CHandlingDataMgr/HandlingData/Item[@type="CHandlingData"]/handlingName[.="BUFFALO"]/../fMass">

With Double quotation marks "", not Single ''

[phongvants123]

<xml path="common\data\handling.meta">
	<replace xpath='/CHandlingDataMgr/HandlingData/Item[@type="CHandlingData"]/handlingName[.="BUFFALO"]/../fMass'>
		<fMass value="999999.000"/>
	</replace>
</xml>

should be

<xml path="common\data\handling.meta">
	<replace xpath="/CHandlingDataMgr/HandlingData/Item[@type='CHandlingData']/handlingName[.='BUFFALO']/../fMass">
		<fMass value="999999.000"/>
	</replace>
</xml>

i changed the quotation marks to apostrophes .and it worked perfectly