Assign a script to a variable?

http://answers.unity3d.com/questions/209050/assign-a-script-to-a-variable.html

I found this answer on the subject, but it would appear I'm doing wrong here.

In the scene I have an object called _LevelMaster with a script named "LevelMaster" attached too it.

I want my enemy's to grab that script and set it to a variable so they are not constantly using .GetComponent.

in their script I have;

 private var levelMasterScript        : LevelMaster;

It doesn't spit out any errors, but when it's time to grab from that script, something like;

 levelMasterScript.enemyCount -=1;

I get NullReferenceException...

What am I doing wrong?