Maybe it's not SP1 itself but SP1 in combination with something else? I don't see anything related in Windows XP Post-SP1 Hotfixes at http://support.microsoft.com/default.aspx?scid=/support/ServicePacks/Windows/XP/Post-SP1_Hotfixes.asp

>I had it fail on three separate PC's with XP SP1, without XP SP1 it worked fine on two. Our network people use ghost installations for PC's and I thought it possible something is wrong with that as we did identify a problem a few years ago with the installation they were using and communication problems. I don't have the resources to do a fresh install of XP from scratch to test.
>
>
>