Any idea what this is?

[Knipples]

I keep getting (I say keep getting like maybe half a dozen times a day) this message pop up on my yahoo email page, it only happens when im reading/checking email but I have no idea what it is

A script on this page may be busy, or it may have stopped responding. You can stop the script now, or you can continue to see if the script will complete.

Script: http:// mail.yimg.com/d/combo?/mg/6_1_1/js/yui_utils.js&/mg/6_1_1/js/core.js&bc/bc_2.0.4.js&/mg/6_1_1/js/darla.js&/mg/6_1_1/js/async.js&/ult/ylc_1.9.js&/ mg/6_1_1/js/imboot.js&:1

I click on stop script, and tick the box thats there for "Do not show this message again" but it comes back again.

Does anyone have a clue what it might be?