The dreaded 'long-running script' message should theoretically only appear when there's an error with the coding of the site that you're visiting. However in practice it generally occurs when either your browser or something else on your computer is hogging all of its resources, leaving it with insufficient capacity to fully download and display the page you want to see. Taking a look at the processes running when it happens can often tell you whether it's your browser or something else (such as a Windows update) that's hogging all of your PC's resources. (Go into Task Manger, via right-clicking on the task bar at the foot of your screen. to see what's eating all of your memory or CPU power).
Resetting your browser to it's 'out of the box' settings, or simply flushing its cache, often fixes the problem though. (Tell us which browser you're using if you require instructions).
However, as Alavahalf says, it might be worth trying a different browser anyway. I've recently switched from Firefox (which I still like) to Slimjet as my main browser:
https://www.slimjet.com/