Issass.exe

Friends ,, I am new to few problem with win xp . so need me some help fron u all.
What is remote procedure call ? Why it is important for winxp while running Internet connection.
I am getting a few problem with rpc. the problems are listed bellow..............

shutdown
The system will shutdown, u will lose any unsave datas. the shutdown was initiated by NT AUTORITY/SYSTEM.

MESSAGE
Windows must now restart because the remote procedure call service terminated u expectedly.
..........
And another message is .......
message
The system program c:\windows\system32\Issass.exe terminated unexpectedly.

One of my friends on the net called me that this is due to some virus called "sasser" virus.
But I am not satisfy with this information as I got this problem at sevaral PCs after I install
a network cable connecion and winproxy 2.1. I ask our ISP if there is any virus at there server .. but they deny so. I even don't make any changes with the setting of my winprocxy connection.
Sometimes it connect and work well. but it several time give me problem . If there any one to help me in detail please .Thanks for ur all efforts.