Please check your checkinstall folder in $install/checkinstall and open the $install\checkinstall\check-logs\precheck-results.html.
Check the ERROR result for check-lang-locale-setting.xml. Most likely the 'admin' user is set to have a different language from English - you will have the exact error message there.
If the issue is with the language, please reset the admin's user language and try the upgrade again.
If not, and it's not explicit enough for you to address, please provide the exact error message and precheck-results.html for review to CA Support.