How do i add another file ('thumbs.db') to the exclude list when performing a directory comparison?

It already has '.DS_Store' in the field.

Do i just put a space between the 2 filenames?
Or a comma?
Or something else?

I am creating an XML in .net using XmlTextWriter to attach as a file in Dynamics. When I try to test the file I get the error - Unable to parse any XML input. Error on line 1: The markup in the document preceding the root element must be well-formed. If I open the file in notepad++ and copy and past...