If I change nas0.tclc.org to a different IP, say 10.1.1.81, then dir \\nas0.tclc.org\d0 still fails.

So, any inspection of nas0.tclc.org works everywhere, but any use of nas0.tclc.org fails only on Windows, regardless of the value. I no longer suspect a corruption, since I have purged and reinitialized all known sources and caches. This may be a collision, but that would require some rogue assignment that I haven't found. It may also be a permissions problem, but domain name level permissions is easily checked and I compared this name with nas1.tclc.org, which is not known to have problems. Ultimately, the culprit will have to be the NAS, since this all happened, coincidentally, after a system update. I have review all the settings for the NAS, and I have found nothing.