I am calling a stored proc to get back a DS of data:

CREATE PROCEDURE wit_GetPickListData
	@ItemType	VARCHAR(20)

AS
BEGIN

	SELECT ItemKey, ItemType, Caption, ItemDesc
		FROM wit_PickLists
		WHERE ItemType = @ItemType
		ORDER BY Caption

END

I then bind the data set to a listbox and a text box:

// Bind the data set to the listbox
lstItems.DataSource = dsItems.Tables[0];
lstItems.DisplayMember = "Caption";

lstItems.SelectedIndex = -1;

// Bind the caption
txtCaption.DataBindings.Add("Text", dsItems.Tables[0], "Caption");

After I change the value in the textbox I can see te change in the DS using the visualizer. I call UpdateDataSet:

public void UpdateDataSet(DataSet oDS, string sTableName)
{
    if (sTableName == null)
    {
        sTableName = oDS.Tables[0].TableName;
    }

    DataTable oTable = oDS.Tables[sTableName];

    foreach (DataRow oRow in oTable.Rows)
    {
        oRow.EndEdit();
    }

    try
    {
        _oAdapter.Update(oDS, sTableName);
    }
    catch (SqlException e)
    {
        throw e;
    }
}

It's erroring with "Procedure or function 'wit_GetPickListData' expects parameter '@ItemType', which was not supplied."

I don't understand this at all. Why does .Net care about this proc at this point?? What am I doing wrong here???