This was solved with the (offlist) help of Apostolos. It was caused by greek hyphenation patterns, although installed, were not activated in the MiKTeX language.dat file (<root>\tex\generic\config\language.dat). I re-enabled them and through MiKTeX Options (tab Formats) I also enabled xetex and xelatex, building the format files, and all was well.
Thanks Apostole! -- The jewel that never leaves the mine is never polished. -- Saadi -------------------------------------------------- Subscriptions, Archive, and List information, etc.: http://tug.org/mailman/listinfo/xetex
