help with parameters please

Hi,
I am very new to Alice and have the handicap of not being into video/computer games. I have to take the class in order to get at my IT core classes. Can anyone clue me in on how to add parameter to a method that I already created? The assignment says to add 3 parameter to a given method -- I get the subject must not be null error message after I set up the method and try to create the next parameter. What am I doing incorrect? What does the error message mean?

Thank you,
Jen

Sorry, I was going to add some pictures, but they turned out to be pretty bad quality. I'll walk you through it though.


-First you Click on "Make a parameter" which is a button to the right of every method.

-A window should pop up, Select what type of Parameter you want, for examle: Number, Boolean,Object, or you can click other for more options.

-Name the Parameter, and click "O.K."

-when you put the method into the world, make surre you change the parameter to whatever you want it to be.