Problem:
SPN validation failed
Failed to modify SPNs on CN=pc13-204,OU=Windows7,OU=PC,OU=Schein,DC=schein,DC=ig: acl: spn validation failed for spn[MSSQLSvc/PC13-204.schein.ig:SQLEXPRESS] uac[0x1000] account[PC13-204$] hostname[PC13-204.schein.ig] nbname[SCHEIN] ntds[(null)] forest[schein.ig] domain[schein.ig]
Solution:
samba-tool spn list PC13-204$
does not show the SPN MSSQLSvc/PC13-204.schein.ig:SQLEXPRESS
So you can do this manually
samba-tool spn add "MSSQLSvc/PC13-204.SCHEIN.IG:SQLEXPRESS" PC13-204$
Make sure you use the domainname in capitals.