check box disables radio buttons

I think you may be using WPF as the parameter e in the method signature is of type RoutedEventArgs. If so, then the CheckBox control of WPF has got Checked and Unchecked events as explained here.
WPF CheckBox Events[^]

You are handling only the Checked event of the CheckBox, hence desired action takes place when the CheckBox is checked and nothing happens when the CheckBox is unchecked as the Unchecked event is not handled.

The Checked and Unchecked can be used as follows

void chkbox_Unchecked(object sender, RoutedEventArgs e)
{
   acceptRadioButton.IsEnabled = true;
   declineRadioButton.IsEnabled = true;
}

void chkbox_Checked(object sender, RoutedEventArgs e)
{
   acceptRadioButton.IsEnabled = false;
   declineRadioButton.IsEnabled = false;
}

Try this...

protected void CheckBox1_CheckedChanged(object sender, EventArgs e)
   {
       if (CheckBox1.Checked== true)
       {
           RadioButton1.Enabled = false;
           RadioButton2.Enabled = false;
       }
       else
       {
           RadioButton1.Enabled = true;
           RadioButton2.Enabled = true;
       }
   }

<div>
   <asp:CheckBox ID="CheckBox1" runat="server" OnCheckedChanged="CheckBox1_CheckedChanged" AutoPostBack="True" /><br />

  <asp:RadioButton ID="RadioButton1" runat="server" />
  <asp:RadioButton ID="RadioButton2" runat="server" />
      </div>

Check For Unchecked event of checkbox in the event list of check box

Hi,

If you are using ASP.NET, then you have to set the

AutoPostBack

property of checkbox to

True