Explain how each element is located with respect to the main timeline. You said that resultText is a movie clip textbox, but your code doesn't indicate that. It is targeting it as just a textbox, not a movieclip containing a textbox. If it was a mmovieclip textbox then the code would look more like...
_root.over_mc.finalResultText.text = text_mc.resultText.text;
Where text_mc represents whatever instance name of the movieclip that has the textbox
ok.. for ResultText.text right.. it is a hidden textbox located in a main timeline.
then for FinalResultText.text, it is located at a movie clips.
I'm doing an application when i click on the search button, it will pass the variable for ResultText.text to the FinalResultText.text.
If the button is loactaed on the main timeline, then the code you showed may be correct...
over_mc.finalResultText.text = resultText.text;
though your instance names are questionable since you are spelling them differently between your first and second postings (capital letters?). So make sure you are using the names properly. Also, you may want to put a trace inside the search button code to make sure that it is working as a button.