Solved
Invalid class string: cannot obtain ClassID.
I am trying to do this example: https://support.smartbear.com/testcomplete/docs/testing-with/advanced/working-with-external-data-sources/files/xml.html
TestWithXPath(): but in the line Doc = Sys.OleObject["Msxml2.DOMDocument.4.0"] appear the error Invalid class string: cannot obtain ClassID.
It's possible that you don't have version 4.0 of MSXML2 installed.
Change that line to
Doc = Sys.OleObject["Msxml2.DOMDocument"]
and try again
