Indeed, Virus Chest needs RPC service to be running. Do you see: ashServ.exe and aswUpdSv.exe in the system services (formely Services applet of the Administrative Tools in Control Panel).

Do you see RPC (Remote Procedure Call)? RPC is Remote Procedure Call.
There are various configurations mentioned at http://www.blkviper.com/WinXP/servicecfg.htm to shutting down and disabling many of Microsoft’s services which you may do not need. But
these actions - disabling Windows Services - is quite an advanced task. Avast! requires at least RPC service running… You can cause more conflits doing so. Be smart! Good luck. If you need more help, tell us.

Try to desinstall, boot and install avast again.
If this not work, please see Administrative Tools / Services
and look what is marked to RPC Service. It must be Start Automatically.
Both avast Services must be setted to start automacatilly either…

Btw, RPC is indeed an independent service of NT/XP systems. Just search the word ‘RPC’ in forums, you´ll get some:
This forum includes ZoneAlarm and RPC discussion
This one includes a picture of RPC Window
This is specific of RPC error

Other foruns:
http://www.avast.com/forum/index.php?board=2;action=display;threadid=695;start=msg3360#msg3360
http://www.avast.com/forum/index.php?board=2;action=display;threadid=1550;start=msg9463#msg9463
http://www.avast.com/forum/index.php?board=8;action=display;threadid=1461;start=msg8651#msg8651
http://www.avast.com/forum/index.php?board=2;action=display;threadid=1321;start=msg7437#msg7437
http://www.avast.com/forum/index.php?board=2;action=display;threadid=1311;start=msg7227#msg7227
http://www.avast.com/forum/index.php?board=2;action=display;threadid=1311;start=msg7225#msg7225
http://www.avast.com/forum/index.php?board=2;action=display;threadid=1243;start=msg6772#msg6772
http://www.avast.com/forum/index.php?board=2;action=display;threadid=1121;start=msg6077#msg6077