using timer to hide panel

I try to use timer to hide a panel by clicking the button, if invalid, it will show 'cannot', then after 2 seconds, the word 'cannot' will disappear with the panel invisible. However, 'cannot' still cannot disappear.
protected void button01_Click(object sender, EventArgs e)
{

ccJoin.ValidateCaptcha(txtCap.Text);
if (!ccJoin.UserValidated) Go to the complete details ...