Please try the following from linux shell:
fwconsole mysql
select * from sysadmin_options where sysadmin_options.key like 'tz%';
You should see two entries:
+--------------+---------+
| key | value |
+--------------+---------+
| tz_continent | America |
| tz_region | Chicago |
+--------------+---------+
If either of these are wrong, do the following from within MySQL:
update sysadmin_options set value='America' where sysadmin_options.key='tz_continent';
This will change the continent to ‘America’. To change the region:
update sysadmin_options set value='Chicago' where sysadmin_options.key='tz_region';
That will give you CST. See if that gets you into the GUI again, and then adjust the settings from sysadmin as needed. Type exit to leave MySQL.