Newbie respond_to question

I am sending data from a grid back to /configuration/edit/id

This works, the data gets to the server.

The problems is that my jQuery setup:

    url: '<%= params[:id] %>.json',
    contentType: "application/json",
    dataType: "application/json",
    success: function(msg) {
      console( "Data Saved: " + msg );

and controller

    respond_to do |format|
        format.json {
            # some logic here
        format.html { render :action => 'edit.html.erb' }

gives me an ActionView error.

So, data goes to server from jQuery, but then the server side error.
No idea why it's reverting to edit.erb

Any help appreciated.