bundle does not contain any mapped documents/entities

This will be an error you would see when trying to generate entities or documents using:

app/console doctrine:mongodb:generate:documents YourPathToBundle

Actually the error would also suggest if you have mapping annotation error.

Mostly this could arise from mapping error as suggested.. check if you have @MongoDbDocument in the case of document or the respective @ORMEntity that would tell what that Plain Old Php Object is representing..
btw, the MongoDb and ORM are the aliases, so it could different on your setting..