Question : Once I installed service pack 3 I can no longer access the shared files folder

I am not sure if it was enabled before, or if when I installed SP3 it enabled the firewall, but now I can access that computers shared files unless I turn off the firewall.  Is there an exception to add or?

Answer : Once I installed service pack 3 I can no longer access the shared files folder

I have had this same problem and here is the solution that seems to have worked for me. It has to do with the addition of NAP (network access protocol) added with SP3.  Apparently NAP doesn't run, so access is denied... strange setup.  You just have to tell the XP computer to run NAP automatically.  When I turned it on, I regained access to shared files.

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Start > Run > Services.msc

Change the Network Access Protection Agent service to start automatically

Start the Network Access Protection Agent service
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Hope that works for everyone else with this problem!