Clear your browser cache and cookies, log into store and try to download again.
If that doesn't work contact Cakewalk support:
http://www.cakewalk.com/support/contact/default.aspx If for some reason you have problems registering Dimension Pro afterwards run Sonar X1/2 as Administrator.
(nb Cakewalk is way overdue for an update to this software, some people have no issues, but it's probably the buggiest plugin when it comes to installation).
NB Might be worth checking to see if the right files are in the VST folder, might be another post about this if you search the forums.