First, throw away the installer for which the disk image fails to mount. Go ahead and empty the trash as well.

In your Utilities folder in the Applications folder you will find the disk utility. Launch that application and choose "Repair Permissions". You'll find a button for this option toward the bottom. It will take a couple of minutes to complete.

Then, Restart your Mac. After restart, download Limewire again. The disk image should mount successfully.