Problem when multi-column sorting

How complicated is the application in which this problem is occurring? Our guru suggests that you try it with the simplest possible application if you have not done so. In my case I have a single entity class with only two properties that are bound using the DataGridViewBindingManager. Also, my comparer class is part of the UI startup project and I don't implement any IComparer in the entity class itself.

I tried to reproduce this (sort of) and was unable to do so.

I worked against the Employee table in the IdeaBladeTutorial database and I sort against TitleOfCourtesy and LastName. The idea is that there will be more than one person with the same TitleOfCourtesy but, in this case, no two Employees with the same LastName.

The code I use to populate the BindingSource looks like this:

        private void Form1_Load(object sender, EventArgs e)
        {
            mPm = PersistenceManager.DefaultManager;
            employees = mPm.GetEntities<Employee>();
            employees.ApplySort(new EmployeeTitleNameComparer(), true);
            employeeBindingSource.DataSource = employees;

        }

My IComparer implementation looks like this:

    class EmployeeTitleNameComparer: IComparer<Employee>
    {
        public int Compare(Employee pEmployee1, Employee pEmployee2)
        {
            if (pEmployee1 == null || pEmployee1.IsNullEntity && pEmployee2 == null || pEmployee2.IsNullEntity)
            {
               return 0;
            }
            if (pEmployee2 == null || pEmployee2.IsNullEntity)
            {
               return -1;
            }
            if (pEmployee1 == null || pEmployee1.IsNullEntity)
            {
               return 1;
            }
            if (pEmployee1.LastName == pEmployee2.LastName)
            {
               return 0;
            }
            int i = (String.Compare(pEmployee1.TitleOfCourtesy, pEmployee2.TitleOfCourtesy, true, System.Globalization.CultureInfo.CurrentCulture));
            if (i == 0)
            {
               return (String.Compare(pEmployee1.LastName, pEmployee2.LastName, true, System.Globalization.CultureInfo.CurrentCulture));
            }
            else
            {
               return i;
            }
        }
    }

I don't get the exception and the sort works as I expect.

I suspect that the problem is actually somewhere other than in the sort. Lacking any better ideas, I would suggest that, as a start, you comment out the line where you apply the sort and see if you still get the exception.