As far as I can see, you really need to know the specifics of the XML dialect being used, probably XHTML in this case. Maybe it has been mixed up with HTML proper, or your translation tool has mangled the tags. Best thing you can do is to tell your engineer to load the file into an XML-capable source editor (there are free ones out there) which is able to validate against the DTD/schema or whatever is providing the syntax. Though it is questionable whether this would provide you with anything that you don't know already.
Anyway, a good validating editor should allow you to see errors being corrected as you type. But you still need to have an idea of how the DTD works in order to do that. I see no way around that (other than letting your client sort it out) -- maybe others do.
[Edited at 2010-05-18 22:58 GMT]