What is "unresponsive script?"

You really haven't given us any context at all. What are you exactly doing when the message comes up.

I'm going to assume that it happens when you're browsing the internet. If so then what is the browser you use? Has it been updated lately? Ever been updated?

It could be some glitch or conflict between your browser and say Javascript on the page you're viewing.

You probably went to a webpage with bad javascript (where bad probably means stupid rather than malevolent).

If simply closing the offending page down doesn't work, then I would close down the browser. That means completely close it down (i.e. use quit especially if you are on a mac).

Then bring the browser back up again (avoiding the offending page of course).

That should fix it.