try this
protected void CBContacts_SelectedIndexChanged(object sender, EventArgs e)
{
txtFacebook.Visible = false;
txtLinkedIn.Visible = false;
txtSkype.Visible = false;
txtTwitter.Visible = false;
foreach (ListItem item in CBContacts.Items)
{
if (item.Selected)
{
switch (item.Text)
{
case "facebook":
txtFacebook.Visible = true;
break;
case "twitter":
txtTwitter.Visible = true;
break;
case "Linkdln":
txtLinkedIn.Visible = true;
break;
case "Skype":
txtSkype.Visible = true;
break;
}
}
}
}
<asp:CheckBoxList AutoPostBack="true" ID="CBContacts" runat="server" OnSelectedIndexChanged="CBContacts_SelectedIndexChanged">
<asp:ListItem Text="facebook" />
<asp:ListItem Text="twitter" />
<asp:ListItem Text="Linkdln" />
<asp:ListItem Text="Skype" />
</asp:CheckBoxList>