Turn off UAC
Run everything with 'as admin'
Has the DB2Admin account been added to the local Administrators group as this should have occurred.
The db2admin account must not already exist on install of db2. No idea why or what problems would occur. The same for the groups it creates. So maybe clean up all this too.
The db2admin password should not be longer than 8 characters.
The db2admin password must meet any OS / GP password complexity rules.
The db2admin password must not contain special characters.
On creating the db2 database, the name must not be the same as the host / ssc name. The name must be like a unique DNS entry.
Log on as the local DB2Admin account to perform the SSC installation.