KRB5_REALM_UNKNOWN errors with GSS Negotiate on Vista

[David Rosenstrauch]

I'm experiencing "Cannot find KDC for requested realm" 
(KRB5_REALM_UNKNOWN) errors when running our code on Windows Vista.  But 
on XP the exact same executables work fine.  Very strange.  What's even 
stranger is that this code used to work fine on the Vista box too until 
we had to reinstall the OS.  Details as follows:

Our code uses libcurl for http requests.  We've built libcurl with 
support for GSSAPI/SPNEGO, using the appropriate libraries, including 
MIT Kerberos (i.e., gssapi32.dll, etc.).  All was working well - code 
ran fine on both Vista and XP.

... until about a week ago, when problems on the Vista box forced us to 
reinstall the OS.  Now libcurl is tossing up "Cannot find KDC for 
requested realm" messages from krb5 whenever we access an 
SPNEGO-protected site.

I'm at a bit of a loss to understand what the error even is here.  IIUC, 
KRB5_REALM_UNKNOWN errors mean that krb5 was not able to locate the KDC 
via SRV DNS records.  But I don't understand how that could be the case. 
  I've verified that the records are there.  Plus the XP box (which is 
part of the same domain) obviously looks them up just fine.  So I'm 
wondering what's unique about Vista - or perhaps this particular Vista 
box - that would prevent krb5 from finding it?  (And similarly, what 
might have changed on the Vista box since the OS re-install that broke 
it?)  Google turned up a whole lot of nothing.

Help appreciated - I'm stumped!

TIA,

DR