file was blocked after download completes (problems after downloading LW)

[tristat]

i paid for limewire and when click on the save button and download the limewire program it all goes well download completes then a box pops up saying ......Windows has found a problem with this file this file was blocke because it does not hav a valid digital signature that verifys its publisher i have a new laptop with vista and norton security....im sure this is a easy fix and hope someone can help thanks