yahoo messenger keeps going offline by it self?

my office use 2 internet network from different provider, each have more than sufficient bandwidth. The problem persist on both network ( I even had tried directly without my proxy server). Because of the problem we’re having with ym, my colleague (and me) prefer to use pidgin (or gaim), trilian, even miranda (they never stalled like ym). We’ve tried many version of ym, starting from 6 to 9 beta. and the problem persist. ym keeps bouncing offline-online-offline-online all the time. Anyone knows why is this happening?
My network cables and internet connection is fine. the proxy setting is fine ( I’m one of the administrator). The one that amaze me is the irony where yahoo messenger (from yahoo) works badly in their own network compared to pidgin or trilian (3rd party). sigh..

call a computer person

Electro playing a 2v2