datagridview column names

[Bill Cart]

I have a datagridview that was created by dragging an SQL stored procedure
onto the form. The SQL query has fields for Monday, Tuesday, etc.

I am trying to set some of the values with the DefaultValuesNeeded event.
When I right click on the control and select Edit Columns I can see a column
that appears to be named Monday.

The code is:
private void spApplicantMealListDataGridView_DefaultValuesNeede d(object
sender, DataGridViewRowEventArgs e)
{
e.Row.Cells[9].Value = ThisClientId;
e.Row.Cells["Monday"].Value = 0;
}

When I run the program I get an error: {"Column named Monday cannot be
found.\r\nParameter name: columnName"}

I go into Edit columns and Click on Add new column and select Monday as a
DataBound column. I add the column and then I see two columns that appear to
be named Monday. I run the program and then it works and shows the correct
data in both of the columns!! I can delete the original column and it works
correctly from then on.

Why? What are the default names for the columns?