can u give us more info?
from where u downloaded the .sis file , how are u trying to install them .... ?
if they are compatible?
also try downloading themes from those websites :
http://www.symbianthemes.us/nokia_n85/ http://www.mmcforums.net/theme/nokia-N85-themes.html
just try few themes from those websites if still not working ... u have a big problem :D