Using Windows 8.1 HP PC, Firefox Browser
Running WordPress 4.2.3 running StartupWP theme Pro Version
Cleared Firefox cache
Deactivated all plug-ins
StartupWP and WordPress credits are not removed by default
With your help the problem is solved.
1st I logged out of wp-admin for my original domain which was using the Startup Pro theme.
Then I uploaded the Startup Pro theme while logged into my 2nd domain. It installed and activated successfully.
Thanks for your help.