Strings and Variables

Hopefully this wil be enough of an explaination but if not i can detail my question further.
Okay i have some code that analyses a string and does some stuff, spliting and joining etc.

if i have this:
var uploadString:String = new String(“160524”);
all is cool in my world

BUT

if i have this:
var uploadString:String = new String(_root.myStringSmart)

then everything breaks, is it because flash doesnt know that my root variable is in fact a string and as such anything i do to i it cant understand.

hopefully that will be enough info regarding this query, if anyone out there is a string genious please help!