File format unknown?

I have a Nokia 7310 Supernova. I have tried twice to download a theme for my phone but both times I get an error message saying 'file format unknown' I don't understand why because the default themes are the same file format - nth.

Anyone know why this might be happening? Any help will be much appreciated.

Brother,click home folder,then click download folder,then click free theme for nokia 7310supernova.Then try to download ur file.If it is still corrupted,then contact moderator:thumbsup:

First off thanks for replying.

Sorry for being dense but where is the home folder?