Here's a fix from the Symantec Technical Support Knowledge Base.
You can also restore LiveUpdate and Symantex AntiVirus operation by adding
exceptions to the firewall:
Windows XP Professional, SP2 Systems
Add WXP ICF Service Exceptions for Symantec AntiVirus
1. Right-click My Network Places, {Properties}
2. Right-click Local Area Connection, {Properties}
3. Local Area Network Properties
Click Advanced tab
Under Windows Firewall, {Settings…}
4. Windows Firewall
Click Exceptions tab
5. Windows Firewall, Exceptions tab
Under Programs and Services, {Add Program…}
6. Add a Program
Select Symantec AntiVirus
{OK}
7. Add a Program, {Browse…}
8. Browse
C:\Program Files\Symantec AntiVirus\Rtvscan.exe
{Open}
9. Add a Program
Select Rtvscan
{OK}
10. Windows Firewall, Exceptions tab
Under Programs and Services, {Add Program…}
11. Add a Program, {Browse…}
12. Browse
C:\Program Files\Symantec \LiveUpdate\LuCommServer.exe
( or Lucomserver_2_5.exe or Lucomserver_2_6.exe)
{Open}
13. Add a Program
Select LuComServer (or _2_5 or _2_6)
{OK}
14. Windows Firewall, Exceptions tab, {OK}
15. Local Area Network Properties, Advanced tab, {OK}
16. Close Network Connections window