Преобразование из строки "DGL/C-2905" в тип "double" недопустимо.

First Entry is accepted on auto generate ID as DGL/C-2905. But After there is error as "Conversion from string "DGL/C- 2905" to type 'Double' is not valid."

Please advice if i need any correction on my coding.

Data Table column Name ClientID and Datatype - nvarchar(50)

Private Sub Autogenerated_Id()
        Dim Cmd As New SqlClient.SqlCommand
        Dim Con As New SqlClient.SqlConnection
        Con.ConnectionString = "Data Source=(localdb)\MSSQLLocalDB;Initial Catalog=dbase;Integrated Security=True;Pooling=False"
        Cmd.Connection = Con
        Con.Open()
        Dim Number As Integer
        Cmd.CommandText = "Select Max(ClientID) from Client"
        If IsDBNull(Cmd.ExecuteScalar) Then
            Number = 2905
            Tbcltid.Text = "DGL/C- " & Number
        Else
            Number = Cmd.ExecuteScalar + 1
            Tbcltid.Text = "DGL/C- " & Number
        End If
        Con.Close()
    End Sub