ASP.Net Error: Violating the Primary Key constraint. can not insert the duplicate key into the object

hi, 

can you help me to take a look of my code why i got an error of the duplicate key.  thanks. 

        DBConnection.Open()
        DBCommand = New SqlCommand("QStudentCWIDCheck_sp", DBConnection)
        DBCommand.Parameters.AddWithValue("@StudentCWIDCheck", StudCWIDtxt.Text.ToString())
        DBCommand.CommandType = CommandType.StoredProcedure
        DBReader = DBCommand.ExecuteReader()

        'If DBReader.HasRows Then
        If DBReader.Read() Then
            If StudCWIDtxt.Text = DBReader("StudCWID") Then
                'lblerror.Visible = True
                'Exit Sub

                DBConnection.Close()
                DBConnection.Open()
                DBCommand = New SqlCommand("QStudentRecordUpdateFieldwork_sp", DBConnection)
                DBCommand.CommandType = CommandType.StoredProcedure

                DBCommand.Parameters.Add("@StudentCWID", SqlDbType.NVarChar, 9).Value = StudCWIDtxt.Text
                DBCommand.Parameters.Add("@StudentTermID", SqlDbType.NVarChar).Value = SemTerm
                DBCommand.Parameters.Add("@StudentYearID", SqlDbType.NVarChar).Value = SemYear
                DBCommand.Parameters.Add("@StudentInstructorName", SqlDbType.NVarChar, 50).Value = FacID.Text
                DBCommand.Parameters.Add("@StudentOPAddress", SqlDbType.NVarChar, 225).Value = Addresslbl.Text
                DBCommand.Parameters.Add("@StudentOPPhone", SqlDbType.NVarChar, 50).Value = OPPhonelbl.Text
                DBCommand.Parameters.Add("@StudentSupervisorName", SqlDbType.NVarChar, 50).Value = Supervisorlbl.Text
                DBCommand.Parameters.Add("@StudentFWCourse", SqlDbType.NVarChar, 50).Value = DropDownList1.SelectedValue
                DBCommand.Parameters.Add("@StudentOrgCode", SqlDbType.NVarChar, 150).Value = OrgCodelbl.Text
                DBCommand.Parameters.Add("@StudentOPTitle", SqlDbType.NVarChar, 100).Value = ProgCodelbl.Text

                DBCommand.ExecuteNonQuery()
                DBConnection.Close()
                'End If
            End If
        Else
            DBConnection.Close()
            DBConnection.Open()
            DBCommand = New SqlCommand("QStudentRecordAdd_sp", DBConnection)
            DBCommand.CommandType = CommandType.StoredProcedure

            DBCommand.Parameters.Add("@StudentCWID", SqlDbType.NVarChar, 9).Value = StudCWIDtxt.Text
            DBCommand.Parameters.Add("@StudentOrgCode", SqlDbType.NVarChar, 150).Value = OrgCodelbl.Text
            DBCommand.Parameters.Add("@StudentOPTitle", SqlDbType.NVarChar, 100).Value = ProgCodelbl.Text
            DBCommand.Parameters.Add("@StudentOPAddress", SqlDbType.NVarChar, 225).Value = Addresslbl.Text
            DBCommand.Parameters.Add("@StudentOPPhone", SqlDbType.NVarChar, 50).Value = OPPhonelbl.Text
            DBCommand.Parameters.Add("@StudentSupervisorName", SqlDbType.NVarChar, 50).Value = Supervisorlbl.Text
            DBCommand.Parameters.Add("@StudentUpdate", SqlDbType.NVarChar, 50).Value = Datetxt.Text
            DBCommand.Parameters.Add("@StudentFirstName", SqlDbType.NVarChar, 50).Value = StudFNametxt.Text
            DBCommand.Parameters.Add("@StudentLastName", SqlDbType.NVarChar, 50).Value = StudLNametxt.Text
            DBCommand.Parameters.Add("@StudentCPhone", SqlDbType.NVarChar, 14).Value = CPhonetxt.Text
            DBCommand.Parameters.Add("@StudentTermID", SqlDbType.NVarChar).Value = SemTerm
            DBCommand.Parameters.Add("@StudentYearID", SqlDbType.NVarChar).Value = SemYear
            DBCommand.Parameters.Add("@StudentAddress", SqlDbType.NVarChar, 75).Value = StAddress.Text
            DBCommand.Parameters.Add("@StudentCity", SqlDbType.NVarChar, 30).Value = City.Text
            DBCommand.Parameters.Add("@StudentZip", SqlDbType.NVarChar, 20).Value = ZipCode.Text
            DBCommand.Parameters.Add("@StudentEmail", SqlDbType.NVarChar, 225).Value = Email.Text
            DBCommand.Parameters.Add("@StudentInstructorName", SqlDbType.NVarChar, 50).Value = FacID.Text
            DBCommand.Parameters.Add("@StudentFWCourse", SqlDbType.NVarChar, 50).Value = DropDownList1.SelectedValue

            DBCommand.ExecuteNonQuery()
            DBConnection.Close()
        End If

here is the error.

Violating the Primary Key constraint.  can not insert the duplicate key into the object dbo_Students. and termiate