When an error is encountered in processing an RPC request, most other methods return an array of the form array('status' => '<Some Error Message>'). However, the update_response method instead returns strings.

For consistency reasons, it would be good if this method returned a similar array. It seems like all that would need to be done is update the responses, for example change

return 'Error: No survey response table';

to

return array('status' => 'Error: No survey response table');