This is just something I spent a few hours fixing, thought I'd share.
If you have a woothemes theme an the Screen Options button is not working for you, then I have found a solution. There is a mysql entry in wp_options that disables some buttons in wordpress and here is the fix:
Open phpmyadmin and run the following query on your wordpress database
(be sure to backup first)
DELETE FROM
wp_optionsWHEREoption_nameLIKE ('%woo_maps_default_mapzoom%')