The message - "Number of expected responses exceeded." - occurs when the number of responses is equal to the value set for the "Number of Submissions" option in your Form Settings page. It simply means that the responses to your form has reached the number of allowed responses and would not be receiving more.
To fix this, simply increase the value set in the "Number of Submissions" field. Please note that for validation reasons, you can't remove the value set in the "Number of Submissions" field but you can set it to an extremely high number.