When I turn on preloading of mega menu I receive an error similar to this: "Catchable fatal error: Object of class WP_Error could not be converted to string in /home/wp_jn2d6r/nothingwired.com/wp-content/themes/steam/functions/theme.php on line 648"

Check the following things:

1) Make sure you have one (and only one) primary taxonomy assigned to each minisite.

2) Make sure you have at least one term added inside of the primary taxonomy for each minisite (i.e. the primary taxonomy cannot be empty)