Windows XP Cannot See "Home" Share?

And the offender is: jumbo frames. Why it causes problems with shares that are protected and not open ones, I'm just guessing. But my suspicion is that it initially trys to negotiate using jumbo frames and fails (regardless of share type), then re-negotiates with a standard frame but messes up the credentials (or doesn't re-send them at all). That doesn't bother the open share, but does the protected one.

A couple of weeks ago, I re-aranged my ethernet cabling, and I apparently didn't get it back quite the way it was. I ended up having to go through my WNDR4000 router to get to one NAS but not the other. The WNDR4000 does not support jumbo frames, but my switches do. So, now I was trying to get to the NAS via a device that doesn't support jumbo frames with jumbo frames enabled on the PC. Why it didn't happen right away, I am clueless. My computer typically stays on, but I may have re-booted it for a Windows update or something, and that did it in. It didn't happen on the other XP machine because it's NIC doesn't support jumbo frames. And Win7 or that NIC driver must do a better job with the jumbo frames conflict than the XP one.

After finding that disabling jumbo frames on the PC fixed the issue, I re-checked my wiring and figured out what I changed. Now I'm back to all working with jumbo frames enabled.

Thanks to StephenB in this thread -- http://www.readynas.com/forum/viewtopic.php?f=23&t=61931 -- for the hint that finally got me to the solution.