I have a problem with my new phone. I bought it yesterday and since then I've been trying to put some new themes there. but when I downloaded themes from for example mobile9 that are designed for nokia e66 (something.sis) and put them on my phone, it tries to install them, but fails and writes that it's "failure of certificate". should themes for e66 be something.sis or something.nth ??? why can't i install any of them? thank you for your help.