A first chance exception of type 'System.InvalidCastException' occurred in Microsoft.VisualBasic.dll in vb.NET
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I'm new in Visual Studio and as well as SQL Server. I got confused on how to insert data from visual studio application

I got an error of System.InvalidCastException. I am confused of what is the problem. 

This is my code:

                    PatientInfoConnection.Open() 'open database connection

                    Dim sql As String = ""
                    sql = "insert into model (name, age, date_of_confinement,type_of_sickness, type_of_IVfluid, number_of_bottles, drop_rate)" & _
                                       " values (@name, @age, @date_of_confinement, @type_of_sickness, @type_of_IV_fluid, @number_of_bottles, @drop_rate)"


                    Dim insert As New SqlCommand(sql, PatientInfoConnection)

                    insert.Parameters.AddWithValue("@name", txtName.Text)
                    insert.Parameters.AddWithValue("@age", nudAge.Value.ToString())
                    insert.Parameters.AddWithValue("@date_of_confinement", dtpDate.Value.ToString())
                    insert.Parameters.AddWithValue("@type_of_sickness", txtSickness.Text)
                    insert.Parameters.AddWithValue("@type_of_IV_fluid", txtFluid.Text)
                    insert.Parameters.AddWithValue("@number_of_bottles", txtBottle.Text)
                    insert.Parameters.AddWithValue("@drop_rate", nudDrop.Value.ToString())

                    insert.ExecuteNonQuery()

I am thinking of I got problem with the values. nudAge.Value is numeric up down, in my sql database, it is Age(int, null). I also have dtpDate.Value. A date time picker. I think I should not use ToString() on it but I dont know the syntax.. 

Can anyone help me? Any help would be appreciated. Thanks!