Installer error for VST Set Prologue and Synthesizers on MAC

Hi. I bougtht online downloadable versions of VST Instrument Set Prologue Discoveries and Synthesizers.
I use Cubase Essential 5
I have Mac OSX 10.6.6 on a Mac Book Pro.
I cannot install the Sets because of an error during installation (on both sets!!!) saying: “Installer has encountered an error during installation. Contact software producer for assistance”
What happens?
How can i solve this problem?
I tried new downoloads but the problem persists.
The mac is perfctly clean and updated. No barriers, no gates, no antivirus.

Please, help me