[Samba] Failed to modify SPNs on error in module acl: Constraint violation during LDB_MODIFY (19)

[Markus Dellermann]

Hi,

sometimes I see following in the logs:
/source4/rpc_server/drsuapi/writespn.c:234(dcesrv_drsuapi_DsWriteAccountSpn)
Failed to modify SPNs on 
CN=PCNAME,CN=Computers,DC=DOMAIN,DC=NAME,DC=NAME,DC=de: error in module acl: 
Constraint violation during LDB_MODIFY (19)

In the net i found this "explanation":

"LDAP_CONSTRAINT_VIOLATION 
Indicates that the attribute value specified in a modify, add, or modify DN 
operation violates constraints placed on the attribute. The constraint can be 
one of size or content (string only, no binary)." 

Hm, is this triggerd by dns-updates?
I see this only with two clients
How can I "debug" this ?

I am using samba 4.3.4 with bind-dlz
clients are win7

Thank you for your thoughts!

Markus