Document update conflict

[Stephan Bardubitzki]

I'm using node and cradle to upload and save attachments (in this case 
images), however, I get a

error: conflict
reason: "document update conflict"
status: 409.
The right doc._id and doc._rev attributes are transmitted, what else can 
cause this error?

Here is my server side code:

exports.addLogo = function(req, res) {
    var business,
        businessName = req.body.businessname;
    if ( req.files ) {
        // get business data
        db.view('business/getByBusinessName', { key: businessName }, 
function(err, doc) {
            if ( err ) {
                res.send({ header: 'Upload business logo', message: 
err.reason, type: 'error'});
            }
            else {
                business = doc[0].value;
                // add business logo to couchdb document
                db.saveAttachment(
                    business._id,
                    business._rev,
                    req.files.logo.type,
                    fs.createReadStream(req.files.logo.path),
                    function( att_err, data ) {
                        if ( att_err ) {
                            console.log('Logo upload error: ' + 
att_err.reason);
                            res.send({ header: 'Upload business logo', 
message: att_err.reason, type: 'error'});
                        }
                        else {
                            console.log(data);
                            res.send({ response: 'ok' });
                        }
                });
            }
        });

    }
};