I've seen the same callback 3 times now (that I've been paying attention).  The only difference is the error line that is output when something goes wrong.

You should be able to extract this function out and just have different instances of it.  Something like

``` javascript
function callbackWithErrorMessage() {
  var errArgs = Array.prototype.slice(arguments, 0);
  return function(error, foundGroup) {
    if (error){
      log.error.apply(log, [error].concat(errArgs));
      res.send(500); 
    } else {
      if (foundGroup && groupIsValid(foundGroup)){
        res.send(200,{group : foundGroup});
      }else{
        res.send(204);
      }
    }
  });
}
```