Getting An Error The DELETE Statement Conflicted With The REFERENCE Constraint FK_Detail_Header

Hello All,
i have 2 files in excel which i am uploading them to a folder which is located in the root directory. then i am importing these two files into a sqldatabase. i needed some help in importing them and i got it from my previous post at http://forums.asp.net/t/1261155.aspx
but now i have a problem. the import works perfectly first time but when i do it the second time i am getting an error on of the file (header). to explain clearly, what i am doing is , every time i upload a new file , i am deleting the data from the tables, so the new data can be inserted (  basically trying to achieve overwirting the existing data). now this technique works fine with the Detail table but not with the Header table. i think the reason is the header table has a primary key on OrderID and a relationship does exists between the Header and Detail.
now how would i overcome this error. can some one please guide me. I really appreciate it.
here is my code:
  // connection for header file
protected OleDbCommand headExcelConnection()
{

// Connect to the Excel Spreadsheet
string headConnStr = "Provider=Microsoft.Jet.OLEDB.4.0;" + "Data Source=" + Server.MapPath("~/imports/headerorder.xls") + ";" + "Extended Properties=Excel 8.0;";

// create your excel connection object using the connection string
OleDbConnection headXConn = new OleDbConnection(headConnStr);
headXConn.Open();

// use a SQL Select command to retrieve the data from the Excel Spreadsheet
// the "table name" is the name of the worksheet within the spreadsheet
// in this case, the worksheet name is "Sheet1" and is expressed as: [Sheet1$]

OleDbCommand headCommand = new OleDbCommand("SELECT * FROM [Sheet1$]", headXConn);
return headCommand;


}

// importing header information


protected void BtnImpHeader_Click(object sender, EventArgs e)
{
PanelUpload.Visible = false;
PanelView.Visible = false;
PanelImport.Visible = true;

LabelImport.Text = "";
// reset to blank

// Create a new Adapter
OleDbDataAdapter objDataAdapter = new OleDbDataAdapter();

// retrieve the Select command for the Spreadsheet
objDataAdapter.SelectCommand = headExcelConnection();

// Create a DataSet
DataSet objDataSet = new DataSet();

// Populate the DataSet with the spreadsheet worksheet data
objDataAdapter.Fill(objDataSet);

// deleting the exisitng table before copy
SqlConnection mycon = new SqlConnection(ConfigurationManager.ConnectionStrings["ImportexcelConnectionString"].ConnectionString);
SqlCommand SqlCmd = null;
mycon.Open();
SqlCmd = mycon.CreateCommand();
SqlCmd.CommandText = "DELETE FROM Header"; ---- showing error over on second time
SqlCmd.ExecuteNonQuery();
mycon.Close();

// entering the newer header information

SqlConnection mysqlcon = new SqlConnection(ConfigurationManager.ConnectionStrings["ImportexcelConnectionString"].ConnectionString);
mysqlcon.Open();
foreach (DataRow dr in objDataSet.Tables[0].Rows)
{

String sqlinsert = "insert into Header values(@param1,@param2,@param3,@param4,@param5,@param6,@param7,@param8,@param9,@param10,@param11,@param12,@param13,@param14,@param15,@param16,@param17,@param18,@param19,@param20,@param21,@param22,@param23,@param24,@param25,@param26,@param27,@param28,@param29,@param30,@param31,@param32)";

SqlCommand cmd = new SqlCommand(sqlinsert, mysqlcon);

cmd.Parameters.AddWithValue("@param1", dr[0].ToString());
cmd.Parameters.AddWithValue("@param2", dr[1].ToString());
cmd.Parameters.AddWithValue("@param3", dr[2].ToString());
cmd.Parameters.AddWithValue("@param4", dr[3].ToString());
cmd.Parameters.AddWithValue("@param5", dr[4].ToString());
cmd.Parameters.AddWithValue("@param6", dr[5].ToString());
cmd.Parameters.AddWithValue("@param7", dr[6].ToString());
cmd.Parameters.AddWithValue("@param8", dr[7].ToString());
cmd.Parameters.AddWithValue("@param9", dr[8].ToString());
cmd.Parameters.AddWithValue("@param10", dr[9].ToString());
cmd.Parameters.AddWithValue("@param11", dr[10].ToString());
cmd.Parameters.AddWithValue("@param12", dr[11].ToString());
cmd.Parameters.AddWithValue("@param13", dr[12].ToString());
cmd.Parameters.AddWithValue("@param14", dr[13].ToString());
cmd.Parameters.AddWithValue("@param15", dr[14].ToString());
cmd.Parameters.AddWithValue("@param16", dr[15].ToString());
cmd.Parameters.AddWithValue("@param17", dr[16].ToString());
cmd.Parameters.AddWithValue("@param18", dr[17].ToString());
cmd.Parameters.AddWithValue("@param19", dr[18].ToString());
cmd.Parameters.AddWithValue("@param20", dr[19].ToString());
cmd.Parameters.AddWithValue("@param21", dr[20].ToString());
cmd.Parameters.AddWithValue("@param22", dr[21].ToString());
cmd.Parameters.AddWithValue("@param23", dr[22].ToString());
cmd.Parameters.AddWithValue("@param24", dr[23].ToString());
cmd.Parameters.AddWithValue("@param25", dr[24].ToString());
cmd.Parameters.AddWithValue("@param26", dr[25].ToString());
cmd.Parameters.AddWithValue("@param27", Convert.ToDecimal(dr[26].ToString()));
cmd.Parameters.AddWithValue("@param28", Convert.ToDecimal(dr[27].ToString()));
cmd.Parameters.AddWithValue("@param29", Convert.ToDecimal(dr[28].ToString()));
cmd.Parameters.AddWithValue("@param30", Convert.ToDecimal(dr[29].ToString()));
cmd.Parameters.AddWithValue("@param31", Convert.ToDecimal(dr[30].ToString()));
cmd.Parameters.AddWithValue("@param32", dr[31].ToString());

cmd.ExecuteNonQuery();

// new SqlCommand (stmt, mysqlcon).ExecuteNonQuery();
LabelImport.Text = "Rows Inserted";
}
mysqlcon.Close();


}

// connection for detail file

protected OleDbCommand detExcelConnection()
{

// Connect to the Excel Spreadsheet
string detConnStr = "Provider=Microsoft.Jet.OLEDB.4.0;" + "Data Source=" + Server.MapPath("~/imports/detailorder.xls") + ";" + "Extended Properties=Excel 8.0;";

// create your excel connection object using the connection string
OleDbConnection detXConn = new OleDbConnection(detConnStr);
detXConn.Open();
// create your excel connection object using the connection string

// use a SQL Select command to retrieve the data from the Excel Spreadsheet
// the "table name" is the name of the worksheet within the spreadsheet
// in this case, the worksheet name is "Sheet1" and is expressed as: [Sheet1$]
OleDbCommand detCommand = new OleDbCommand("SELECT * FROM [Sheet1$]", detXConn);
return detCommand;



}

// importing detail information

protected void ButtonImport_Click(object sender, EventArgs e)
{
PanelUpload.Visible = false;
PanelView.Visible = false;
PanelImport.Visible = true;

LabelImport.Text = "";
// reset to blank

// Create a new Adapter
OleDbDataAdapter objDataAdapter = new OleDbDataAdapter();

// retrieve the Select command for the Spreadsheet
objDataAdapter.SelectCommand = detExcelConnection();

// Create a DataSet
DataSet objDataSet = new DataSet();

// Populate the DataSet with the spreadsheet worksheet data
objDataAdapter.Fill(objDataSet);

// deleting the exisitng table before copy
SqlConnection mycon = new SqlConnection(ConfigurationManager.ConnectionStrings["ImportexcelConnectionString"].ConnectionString);
SqlCommand SqlCmd = null;
mycon.Open();
SqlCmd = mycon.CreateCommand();
SqlCmd.CommandText = "DELETE FROM Detail";
SqlCmd.ExecuteNonQuery();
mycon.Close();

// entering newer detail information
SqlConnection mysqlcon = new SqlConnection(ConfigurationManager.ConnectionStrings["ImportexcelConnectionString"].ConnectionString);
mysqlcon.Open();
foreach (DataRow dr1 in objDataSet.Tables[0].Rows)
{
String sqlinsert = "insert into Detail values(@param1,@param2,@param3,@param4,@param5,@param6,@param7,@param8,@param9,@param10,@param11,@param12,@param13)";

SqlCommand cmd = new SqlCommand(sqlinsert, mysqlcon);

cmd.Parameters.AddWithValue("@param1", dr1[0].ToString());
cmd.Parameters.AddWithValue("@param2", dr1[1].ToString());
cmd.Parameters.AddWithValue("@param3", dr1[2].ToString());
cmd.Parameters.AddWithValue("@param4", dr1[3].ToString());
cmd.Parameters.AddWithValue("@param5", dr1[4].ToString());
cmd.Parameters.AddWithValue("@param6", dr1[5].ToString());
cmd.Parameters.AddWithValue("@param7", dr1[6].ToString());
cmd.Parameters.AddWithValue("@param8", Convert.ToDecimal(dr1[7].ToString()));
cmd.Parameters.AddWithValue("@param9", Convert.ToDecimal(dr1[8].ToString()));
cmd.Parameters.AddWithValue("@param10", dr1[9].ToString());
cmd.Parameters.AddWithValue("@param11", dr1[10].ToString());
cmd.Parameters.AddWithValue("@param12", dr1[11].ToString());
cmd.Parameters.AddWithValue("@param13", dr1[12].ToString());

cmd.ExecuteNonQuery();

LabelImport.Text = "Rows Inserted";
}
mysqlcon.Close();

}
 
the error is as follows:


Server Error in '/WebSite6' Application.


The DELETE statement conflicted with the REFERENCE constraint
"FK_Detail_Header". The conflict occurred in database "C:DOCUMENTS AND
SETTINGSMEMY DOCUMENTSVISUAL STUDIO
2005WEBSITESWEBSITE6APP_DATADATABASE.MDF", table "dbo.Detail", column
'OrderID'.
The statement has been terminated. Description:
An unhandled exception occurred during the execution of the current web
request. Please review the stack trace for more information about the error and
where it originated in the code.

Exception Details:
System.Data.SqlClient.SqlException: The DELETE statement conflicted with the
REFERENCE constraint "FK_Detail_Header". The conflict occurred in database
"C:DOCUMENTS AND SETTINGSMEMY DOCUMENTSVISUAL STUDIO
2005WEBSITESWEBSITE6APP_DATADATABASE.MDF", table "dbo.Detail", column
'OrderID'.
The statement has been terminated.

Source Error:






Line 176: SqlCmd = mycon.CreateCommand();
Line 177: SqlCmd.CommandText = "DELETE FROM Header";
Line 178: SqlCmd.ExecuteNonQuery();
Line 179: mycon.Close();
Line 180: 
 again i really appreciate.
Thanks