javascript SQLITE_BUSY: database is locked, sql: insert into "users"

I am working on a 'sign up' page and having trouble with sqlite.

I am using express, bcrypt-nodejs, bookself.js for sqlite. getting an error saying database is lock. any workaround for this? appreciated. below is the code for the part.

var username = req.body.username;
  var password = req.body.password;
  bcrypt.hash(password, null, null, function(err, hash){ 
    new User({'username': username, 'password': hash})
      .save()
      .then(function(){
        console.log('Succesfully saved the user');
      })
      .catch(function(err){
        throw err;
      });
  });