Varible adding problems >_<

Hey guys how ya doing.

Im finishing up a game right now and Im having a simple problem which is getting me frustrated. Its with varibles.

When I put in this code:

_parent.scores = _parent.scores - 500;

I get -500; -1000; -1500;

But when I change the subtract to a plus sign I get:

_parent.scores = _parent.scores - 500;

I get 500; 500500; 500500500;

This code will add correctly on a button, But why when I do this on a onclip handler it does that but it subtracts correctly! >_<

I apoligize If this was solve already in a nother thread but I serached and cant find a solution. It would help me a lot.

Thanks for your time.