You can try using _root.exp for the text field variable, or set the text field in the main timeline.

For AS2 its "_root", for AS3 its "MovieClip(root)".

The alternative and better method would be to use the following code in a frame on the main timeline:

Code:
var exp = 0;
myMovieClip.myField.text = exp; // change instance names to whatever you have