linux4me2 on "Aggregating Usermeta From Blogs To Custom Table"

One thing that strikes me right off is that you have some errors in your array declaration for these two lines:

$data = array(
    'sl_country' => ,
    'sl_image' => ,
);

I'm not sure what data type those fields are in your wp_store_locator table, but you'll need to have values there, not just a space, or PHP will choke. For example, if the country field is a VARCHAR field and you don't have a value you should pass either an empty string (two single quotes, no space) or NULL if NULL is allowed for the field in the database. Same thing for the image field, depending on the data type.

I'd fix that first and see how it works.