Anyway,
In the definition of your stored procedure, there is a @date value that you do not seem to take care of in your code.
You should pass a DateTime to your method and see what happens.
[edit]You may change this line of code:
bool ret = com.AddComment(int.Parse(Request.QueryString["id"]), TextBox1.Text, TextBox2.Text, TextBox3.Text);
[/edit]