Hi,
i had the same problem when trying to install SSO with these options:
create primary node for new vcenter > create the primary node for a new vcenter single sign on installation > use existing supported DB
on the vCenter Single Sign On > Database information window, i failed to connect to the SQL DB.
for me the problem was that i used the $ sign in the account password.
i got to this conclusion reading this post: http://derek858.blogspot.co.il/2012/09/vmware-vcenter-51-installation-part-1.html