Trouble with changing variables

I’m designing a website and I have run into a bit of a snag.
I have a movieclip inside of a button that scrolls a dynamic text in a way that it looks like a news ticker. The dynamic text gets its information from an external xml file.
What I want to set up is a row of buttons, and when you roll over a button the description for that button will scroll in the movieclip i mentioned above.
I thought it would be a simple use of variables to change which text is loaded into the scroller, but I cant seem to get my variable to change on rollover.

If I declare my variable to be a certain number in the first frame, the text scrolls fine, but when I try to have the variable changed by a rollover on a button or simply declared when rolling over the button nothing happens.

Any ideas why this might be or how I can fix it?