I've tried to download it now, and it works just fine so, it's surely a problem on your end.
If you send me an email, I'll send you the file over email.
The addon manager is inside the trial program?
The installer includes everything that needs to be there in order to use the scenery. However, as explained on the Cloud9 page here:http://www.fsdreamteam.com/products_cloud9.html
If the Cloud9 product you purchased doesn't have an FSDT updated installer yet, you have to install the Cloud9 product first, then update the Stand-alone Addon Manager
Since X-City Rome doesn't have an installer from FSDT, it's best to install the scenery and then update the Stand-alone Addon Manager for FSX, using the link provided in the above page.