N96 themes not compatible with N96 phone?

[hehe]

I download N96 themes in many websites, all of them have type "sis", however, when I install on my N96, it has an error " application not compatible with the phone. Continue anyway?". I chose yes, after that,I apply these themes and my phone can't work properly. It stops working and stay the same for a while. I have to format my phone and change back to Nokia original themes. Please help me fix this problem. Thax a lot