Hi Andrew,

Assuming the details in the SPN are correct (eg. it is listening on port 1433, the FQDN has been specified correctly):

Have you restarted the SQL service since adding the SPN?

Have you checked for duplicate SPNs on the server. I saw a server recently on which SQL Server had been reinstalled and a new SPN created. But the old SPN (for a different service account) was still hanging around. It had to be deleted using SETSPN -D.