...was trying to disable:
   <input name="RaddatepickerDDF" id="RaddatepickerDDF" type="hidden" value="2005-01-01" />\n\n   document.getElementById("RaddatepickerDDF").Enabled=false
Which tries to disable a hidden field - not a particularly effective opertation on hidden fields. If you can find the actual input fields that you want to disable, you could theoretically disable those inputs. But the name given to the aspx server control is used to hold the value in a hidden field, which is why your original code doesn't accomplish what you want to accomplish.

Of course, it would be nicer if you could disable the server control - as opposed to handling over on the client. But since that's what your original problem was, you get back to square one.