I went to the Yahoo!Answers Suggestion board on this earlier today and someone had already posted about the problem. Some staffer at Yahoo!U.K. said they meed more details.
I get it whenever a certain ad comes up; It has a gray background with a list of subjects similar to the Y!A subject menu and has at the bottom something like "Powered by Medianet.com".
A script is a piece of programming code / set of instructions / subroutine. If the script enters in a continuous loop it causes the type of problems / messages from the comptuter.
Poorly written scripts can cause the error message you mention as can using an outdated browser.