Dynamic text path problem

alrighty, another problem guys.

I’m trying to affect a dynamic text field which is inside a button on the _root.

text field is called ‘aboutus’
button is called ‘but_about’

So to reference this I tried the code :
_root.but_about.aboutus.text = this.about;
…which is inside a text load function (which works fine)

now this didn’t work so I tried to trace the ._x value of the text field, ie:
trace(_root.but_about.aboutup._x);
and this returns undefined

There’s no masks here and all the fonts are embedded.

Is there an issue with referencing buttons in the same way we do MC’s?

any help would be super! cheers