Ok... your error now reports what the problem is...
Check the Global Announce Mod that you installed. It probably added the "topic_announce_duration" variable in your posting.php file. You have not updated the database to include that variable. Thus, it can't find it, hence the error.
If you have access to phpmyAdmin on your site, just copy the SQL line from the mods install file into the query window and press go. That should solve the problem.