I have done this 5 steps: 1. download file subscript.sty from > http://ctan.org/tex-archive/macros/latex/contrib/fragments. > > > > > 2. Create new folder 'Subscript' in your MiKTeX installation folder (e.g. C:\Program Files\MiKTeX 2.9\tex\latex) > > > > > 3. Copy the file subscript.sty to the folder 'Subscript. > > > 4. Execute as root this comand: mktexlsr
5. Reconfigure LyX. I do not get succesful result. Thank you at all.