Hi,
i am getting the error Expression must evaluate to a node-set. on the following code
oTrans.SelectSingleNode("File/Result").AppendChild(oTemp.SelectSingleNode("//"))

I guess you want
  oTemp.SelectSingleNode("//*")
instead of
  oTemp.SelectSingleNode("//")

i am getting an error
The node to be inserted is from a different document context.
after i changed like this

oTrans.SelectSingleNode("File/Result").AppendChild(oTemp.SelectSingleNode("//*"))

That does not have anything to do with XSLT.
In some DOM implementations you cannot move nodes from one document to another, you need to use ImportNode or AdoptNode.
So assuming you are using the DOM implementation in .NET try
assuming that oTrans is an XmlDocument, or otherwise