Drupal: The First Argument Should Be an Array warning.
When using Drupal, you may get a nasty error like:
"warning: array_key_exists(): The second argument should be either an array or an object in..."
It usually happens when you make DB dump and tar-up files and move all of it to another server/domain.
Quick fix is as follows: you need to log into the database and empty cache by issuing:
delete from cache;
And then you need to access admin/themes page of your website. You may, also, need to go to admin/modules and hit "Save Settings". All of these help Drupal to re-initialize in the new environment and the problem should go away.