The version you’ve downloaded is the Carrara 8.5 “Beta” version,. the Carrara 8 Pro serial number in your account will not work with the Beta, which has a separate Serial number.
With each beta release, there is a different serial number.
The Beta Announcement Thread , (at the top of the forum) had a Link to the Latest Beta release, and the serial Number.
To register the Carrara 8.5 Beta you will need to use the serial code listed here: CDZCPRO-085-0031100-RLS-001-EBTQFSA (Expires September 15th 2012)
Hope it helps