Can't install on Mac OS X: "You should eject the disk image"

Hi,

I'm trying to download and install LoadUI on my Mac. I have tried both 2.0.2 and 2.1.0. I have successfully downloaded the archives and mounted the disk. However, in both instances, when I try to launch the installer I get the following message

“loadUI 2.1.0 Installer.app” is damaged and can’t be opened. You should eject the disk image.

What can I do?

Thanks!

Candide