** FIX & MORE INFO FOR AUTHOR **
I managed to get it working again by doing the following...
1. Disable and delete the SEC plugin in WP admin.
2. Go into phpMyAdmin (through cPanel) and open your sites WP database. Select the 'wp_simple_events' table and export it. (this is the events you may or may not have added).
3. Now delete the entire 'wp_simple_events' table. Then delete any table entries relating to SEC in the 'wp_options' table, I found approximately 7 entries. These entries should look like this... SE_clock, SE_ext_css, SE_timezone, SE_author, SE_links, SE_twitter, SE_db_version.
4. Now you can go back into your WP admin, re-add the plugin (either by FTP or through plugin dash) and activate. You will now see the 'Events' option panel has returned.
5. Now we need to go back into phpMyAdmin, refresh the database / page. You should now see that by re-installing the plugin the 'wp_simple_events' table has returned. All you need to do now is select this table and go up to the import option. We then simply locate the file you downloaded in step 2 and upload it.
and that's it, done!
Not the best way to spend a day but now I have above nailed to just 15 minutes. So until theres a fix I guess this will have to do.
A note to the Author:
When I got the whole thing working again I obviously tried to force it to break again … as any good web dev should do :) and it was all good when I was logged in as the Administrator but then I changed the option "Who can manage events?" to "Editor" and logged in as a user with Editor privileges, I then messed around in the advanced options and this is when it broke again!
Hope this helps :)