Parallels 4.0 says my intel imac is NOT an intel machine

I am trying to upgrade my parallels 3.0 to 4.0 but during the upgrade process a warning comes up that says "Parallels Desktop cannot be installed on your mac. Parallels desktop can only be installed on a intel-based mac. I am using a imac 1.83 Ghz Intel Core duo with OS x 10.4.11. I believe my machine meets the required specs so i am not sure why my upgrade fails.

Any ideas?

Thanks,

s