The object cannot be deleted because it was not found in the ObjectStateManager

It means that entity is not attached (it was not loaded by the same context instance). Try this:

protected MyEntities sqlEntities;public virtual void Delete(TEntity entity){    sqlEntities.Attach(entity);    sqlEntities.DeleteObject(entity);    sqlEntities.SaveChanges();}

Just a small clarification on the answer by Ladislav Mrnka (which should be the accepted answer).

If like me, you've got code in a format like this:

using (var context = new MyDataContext()){    context.MyTableEntity.Remove(EntytyToRemove);    var nrOfObjectsChanged = context.SaveChanges();}

..then this what you want to do:

using (var context = new MyDataContext()){    // Note: Attatch to the entity:    context.MyTableEntity.Attach(EntityToRemove);    context.MyTableEntity.Remove(EntityToRemove);    var nrOfObjectsChanged = context.SaveChanges();}

Perhaps this seems obvious, but it was not clear to me initially that it is necessary to specify the entity to attatch to, and not just the context.

Just to propergate on Kjartans explanation:

I had:

public Project DeleteProject(int id)    {        using (var context = new Context())        {            var p = GetProject(id);            context.Projects.Remove(p);            context.SaveChanges();            return p;        }    }

The problem is that I used my own method (GetProject()) to get the entity (hence using another context to load the entity):

public Project GetProject(int id)    {        using (var context = new Context())        {            var project = context.Projects                .Include(p => p.Reports.Select(q => q.Issues.Select(r => r.Profession)))                .Include(p => p.Reports.Select(q => q.Issues.Select(r => r.Room)))                .SingleOrDefault(x => x.Id == id);            return project;              }    }

One solution could be to attach the loaded entity as Kjartan states, another could be mine solution, to load the entity within the same context:

public Project DeleteProject(int id)    {        using (var context = new Context())        {            var p = context.Projects.SingleOrDefault(x => x.Id == id);            if (p == null)                return p;            context.Projects.Remove(p);            context.SaveChanges();            return p;        }    }