Don't know what FTM GEDCOM file you are using, but an FTM 2014 GEDCOM file, exported as UTF-8, works fine when importing into Genbox for me.
In mid-2012 I exported a GEDCOM from Genbox to FTM 2012, believing FTM would last as a retail genealogy software. When it became apparent that FTM 2014 would not be extended by Ancestry, I produced a GEDCOM file (from FTM 2014, set as UFT-8) to import back into Genbox. Genbox even corrected the lack of sorting by birth order for children in families that FTM 2014 produces in its GEDCOMs.
If you are interested, there are a group of 'die hard' Genbox users on the Genbox mailing list at Rootsweb's software lists.