Dynamic text field in movie clip

meh… I’m stumped…

I can show text in a dynamic text field on my main stage…

But when i put the text field in a movie on the main stage, nada!

On my button i have this actionscript:

on(RollOver)
{ _root.mc-01.letter.text = "b"; }

My movie clip has instance name of “mc-01”, my text field has instance name of “letter”.

I can see the textfield in the debugger and i can point to it using the targetter…

But i get actionscript error when my movie runs:

**Error** Scene=Scene 1, layer=main, frame=1:Line 2:
Left side of assignment operator must be variable or property.

Can anyone shed any light on this? I’m tearing my hair out…