Stop running this script? What's wrong with?

Hi:
There are 5(five) different picture/photo web-sites I've been looking at for long time. However, for the past two or three weeks I'm getting the following error message whenever I trying to look at those pictures.

"A script on this page is causing your web brower to run slowly.
If it continues to run, your computer might become responsive."

Yes No

One of web-sites is 'Rail Pictures Net Photoes USA'

Your help would be greatly appreciated.

Thanks,