This week I had set up our production servers for the migration to SharePoint 2010. I have done this so many times I could do it in my sleep.
We need to use Kerberos Constrained Delegation with ISA 2006. Now setting that up is quite easy but can be complex when something goes wrong. This time I just could not get the Kerberos auth to work. Nothing I did fixed it. I checked everything - except for a duplicate SPN.
setspn -x
found the problem. I had left the SPN registered after my previous test.
This is is how I feel:
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