WLM contacts sign-on alert causes browser playing flash movie to c

Hi all,

Whenever I'm watching shockwave flash video e.g. Youtube videos, in IE 7 or
Firefox, the browsers will crash when my contacts sign-on with live messenger
displaying the alert and playback alert sound.

Upon comparing with another PC that is running fine, it appears that the WLM
add-on for IE needs to be enabled which I've done so. However, it is not
resolving the crashing totally.

My flash player activex for IE is the latest and so is the flash player
plugin for firefox.

Anyone has similar experience and remedy for this weird symptoms?