Here's my error:

```
NHibernate.ObjectNotFoundException: No row with the given identifier exists[Project.Core.Entities.User#(GUID)]
at Hibernate.Impl.SessionFactoryImpl.DefaultEntityNotFoundDelegate.HandleEntityNotFound(String entityName, Object id) 
at NHibernate.Event.Default.DefaultLoadEventListener.Load(LoadEvent event, IEntityPersister persister, EntityKey keyToLoad, LoadType options)

```

One of the users of the system chanced upon getting this error, which doesn't make sense to me entirely. What I do know:

1. A Teacher table REFERENCES a User table.
2. Somehow the Teacher table has a row that references to a row in the User's table, but that row doesn't exist in the User's table.

Any idea why is this happening? Please advise!

Rephrase my Qn:

I know what does the error meant, however I don't seem to figure out what caused the missing user row? I have placed it all on Cascade.ALL. I don't think it's related to deletion. What are the possible scenarios the above may happen?

Edit 2:

Please refer to the mapping via FNH: Any issues with this?

```
public void Override(AutoMapping<Teacher> mapping)
    {
        mapping.References(x => x.User).Cascade.All().Not.LazyLoad();
    }

```

Thanks!