>>>>
>>>>Sorry, I'd forgotten about that behaviour. I guess, if the checkbox and button are at the same level then this would work in the function:

var s = checkbox.id.substr(0, checkbox.id.lastIndexOf("_") + 1) + "btnAgreeContinue"; ;
>>>>var button = document.getElementById(s);
>>>>button.disabled = !checkbox.checked;

but there must be something a bit more elegant.....
>>>
>>>
>>>This didn't work either.
>>
>>Worked for me with a usercontrol in a form but it does depend on both elements being at the same level. Given that, I don't know why it didn't work for you. But it is ugly anyway.....
>
>My two controls are at the same level.
>
>>
>>> I tried my other code to FindControl and pass that in such as this so I could see what the button id was and surprising it is 'btnContinue".
>>
>>So, given that the compiler didn't dream that up from scratch where did the name stem from ?
>>
>>> So very frustrating to get such a simple thing to work. These things make me want to stick to WPF or Silverlight and avoid ASP.net.
>>
>>Very true. Would just have been a simple binding in WPF/Silverlight....
>>
>>>

>>>mmButton thisButton = (mmButton)this.FindControlByName(this, "btnAgreeContinue");
>>>
>>>StringBuilder sb = new StringBuilder();
>>>sb.Append(@"<script language='javascript' type='text/javascript'>");
>>>sb.Append(@"function SetAgreeAndContinue(checkbox) {");
>>>sb.Append(@"var button = document.getElementById('" + thisButton.ID + "');");
>>>sb.Append(@"button.disabled = !checkbox.checked;");
>>>sb.Append(@"}");
>>>sb.Append(@"</script>");
>>>
>>>string myscript = sb.ToString();
>>>Page.RegisterStartupScript("S", myscript);
>>>

>>
>>So what does FindControlByName() look like ?
>
>That was a method someone posted for me here in VB.net and I converted. It works pretty well and does return this control just fine. Here it is again.
>

>public Control FindControlByName<T>(T controlToSearch, string controlID)
>			where T : System.Web.UI.Control
>{
>     Control matchingControl = null;
>
>    try
>    {
>        foreach (Control subControl in controlToSearch.Controls)
>        {
>            if (subControl.ID != null && subControl.ID.EndsWith(controlID))
>            {
>	matchingControl = subControl;
>	break;
>            }
>            else
>            {	
>	if (matchingControl != null)
>	    // found it
>	    break;
>                     else if (subControl.HasControls())
>                    {
>	    matchingControl = this.FindControlByName(subControl, controlID);
>                    }
>            }
>        }
>    }
>    catch (Exception e)
>    {
>        throw;
>     }
>    return matchingControl;
>}
>

Thanks for the code.
But there's no guarantee that the original Id is not duplicated elswhere on the page. So it wouldn't, for example, differentiate between
'ControlA_Control_B_btnAgreeContinue' and 'ControlA_ControlC_btnAgreeContinue' so you couldn't use the same user control twice on the same form.
My version would avoid that problem - or it would if it worked :-{
Did you debug to see where it was going wrong for you ?