MongoLab creates databases that require an authenticated user to access. When you connect with the Shell, you will need to provide the UserName and Password to the shell command. Docs are here.
mongo --username Mark --password something
You will need that Username/Password combination to be configured within mongoose as well. The Mongoose docs have details on the possible ways to do this.
Note that you are using a very old shell. 1.8.3 is about 4 versions back from the current 2.4.* line. This is not directly related to your problem, but it's definitely something you should rectify going forward.