Exchange Messenger problems

Hi people,

in my network, i have almost every machine accesing Exchange instant messaging, using the client 4.6.0079, that works fine on w2000 and windows98, but i have 2 machines windows95 cant sign in, these have IE5.5 sp2, btw i have 2 ANOTHER MACHINES with win95 that can sign in, if the 4 have same TCP/IP configuration, why 2 cant connect?? also, i see they can sign to the .NET (hotmail account) not exchange account, we have a proxy but msmessenger doesnt require it, works with or without proxy.

Whe i reinstall msnmess4.6 display you dont have IE 5.0.

But i have 5.5sp2, please help.