Radio button and set first responder problem

[leelu]

I am building an UI which has 3 radio buttons.

1. Button “Plus” should be highlighted when radio button “1” is selected.
2. Text field “name” should be highlighted when radio button “2” is selected.
3. Button “OK” should be highlighted when radio button “3” is selected.

----------Code-------------------------------------------------------------------------------------------------
on clicked theObject
tell window of the object
if name of theObject is “1” then
set first responder to button “Plus”
else if name of theObject is “New_sheet” then
set first responder to text field " name"
else if name of theObject is “New_book” then
set first responder to button "OK "
end if
end tell
end clicked

The error :
Applescript error: Can’t set «class butT» “Plus” to «class butT» “Plus” o (-10006)

However, the code works fine if I change to use push buttons rather than radio buttons.

Could anyone tell me what I am doing wrong?

Thanks a million!!!