Node.js and MongoDB on MongoLab: "Sockets Closed" On Every Insert - node.js

Question

I'm trying to do something relatively simple and am running into a "server ...-a.mongolab.com:36648 sockets closed" error all of a sudden every time I try to do an "insert".
Reads seem to work without error, but inserts seem to get an error every time and I'm not sure if it's my code (which recently underwent minor changes), or a reliability problem with the free server I'm using at MongoLab (which recently showed itself to be down for a few minutes).
Oddly enough, the record itself seems to save okay, I just get the error back!
Can anyone see an issue with my code, or could this be something else?
var mongoClient = require('mongodb').MongoClient;
var http = require('http');
var connectionString = "...";
var pictureWallsCollectionName = 'PictureWalls';
//this is what barfs. see *** details
exports.saveWall = function (req, res) {
//reformat
var toSave = {
_id: req.body.wallId,
pictures: req.body.pictures
};
var status;
mongoClient.connect(connectionString, function (err, db) {
if (err) { return console.error(err); }
var collection = db.collection(pictureWallsCollectionName);
//*** no err yet... ***
collection.insert(
toSave,
function (error, response) {
//*********************
//*** err here! ******
//*********************
db.close();
if (error) {
console.error(error);
//bad
status = 500;
}
else {
console.log('Inserted into the ' + collection_name + ' collection');
//good
status = 200;
}
});
response.status(status).end(http.STATUS_CODES[status]);
});
}
//this seems to work pretty reliably. including it just in case it's relevant
exports.findByWallId = function (req, res) {
var id = req.params.id;
console.log('Retrieving wall: ' + id);
mongoClient.connect(connectionString, function (err, db) {
if (err) { return console.dir(err); }
var collection = db.collection(pictureWallsCollectionName);
collection.findOne(
{ _id: id },
function (err, item) {
db.close();
if (err) {
console.error(err);
//something bad happened
var status = 500;
res.status(status).end(http.STATUS_CODES[status]);
}
else {
console.log('Found wall with ID ' + id);
//reformat and send back in the response
res.send({
wallId: item._id,
pictures: item.pictures
});
}
}
);
});
};

Answer 1

EDIT: Part of my original issue was duplicate parameter names. See the linked question for detail.
ORIGINAL RESPONSE:
The issue ended up being that I was calling:
res.status(status).end(http.STATUS_CODES[status]);
...before the async insert was finished, so it barfed.
However, I'm not exactly sure how to issue the response in this case. See my new question here:
How Do I Properly Issue Response To Post When Waiting For Async Method To Complete?