disk image not reconized

i’m using an intel mac 10.6.7 with all the requirements for unity, but when i try to download it and mount the disk image, an error pops up saying " the following disk images could not be opened" and cites “not reconized” as the reason

Could be it got corrupted…try re-downloading.

This often happens on accounts without permission to open disk images (a.k.a. you’re not an administrator).

This often happens at my school. >:(

I would contact an administrator about this problem first. If the problem persists, try launching the disk image on another computer with privileges, and copy the installer onto a flash drive to install to the other computer.