A GEDCOM can be edited to change the character encoding. RM7 seems to export in UTF-8. If TNG wants something else, open the GEDCOM in Notepad, click file/save as. At the bottom of the save dialog you'll see a button which offers UTF-8, ANSI, Unicode and Unicode big endian. Choose your poison and save, either with the existing file name or a new one. Your data will be unaffected.
If I were guessing, I'd try Unicode first.